//===--- Expr.h - Swift Language Expression ASTs ----------------*- C++ -*-===//
//
// This source file is part of the Swift.org open source project
//
// Copyright (c) 2014 - 2015 Apple Inc. and the Swift project authors
// Licensed under Apache License v2.0 with Runtime Library Exception
//
// See http://swift.org/LICENSE.txt for license information
// See http://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
//
//===----------------------------------------------------------------------===//
//
// This file defines the Expr class and subclasses.
//
//===----------------------------------------------------------------------===//

#ifndef SWIFT_AST_EXPR_H
#define SWIFT_AST_EXPR_H

#include "swift/AST/CaptureInfo.h"
#include "swift/AST/ConcreteDeclRef.h"
#include "swift/AST/DeclContext.h"
#include "swift/AST/Identifier.h"
#include "swift/AST/Substitution.h"
#include "swift/AST/Type.h"
#include "swift/AST/TypeLoc.h"
#include "swift/Basic/SourceLoc.h"
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/StringRef.h"

namespace llvm {
  struct fltSemantics;
}

namespace swift {
  class ArchetypeType;
  class ASTContext;
  class Type;
  class ValueDecl;
  class Decl;
  class Pattern;
  class SubscriptDecl;
  class Stmt;
  class BraceStmt;
  class ASTWalker;
  class VarDecl;
  class OpaqueValueExpr;
  class ProtocolConformance;
  class FuncDecl;
  class ConstructorDecl;
  class SubstitutableType;
  
enum class ExprKind : uint8_t {
#define EXPR(Id, Parent) Id,
#define EXPR_RANGE(Id, FirstId, LastId) \
  First_##Id##Expr = FirstId, Last_##Id##Expr = LastId,
#include "swift/AST/ExprNodes.def"
};
  
/// Expr - Base class for all expressions in swift.
class alignas(8) Expr {
  Expr(const Expr&) = delete;
  void operator=(const Expr&) = delete;

  class ExprBitfields {
    friend class Expr;
    /// The subclass of Expr that this is.
    unsigned Kind : 8;
    /// Whether the Expr represents something directly written in source or
    /// it was implicitly generated by the type-checker.
    unsigned Implicit : 1;
  };
  enum { NumExprBits = 9 };
  static_assert(NumExprBits <= 32, "fits in an unsigned");

  class LiteralExprBitfields {
    friend class LiteralExpr;
    unsigned : NumExprBits;
  };
  enum { NumLiteralExprBits = NumExprBits + 0 };
  static_assert(NumLiteralExprBits <= 32, "fits in an unsigned");

  class IntegerLiteralExprBitfields {
    friend class IntegerLiteralExpr;
    unsigned : NumLiteralExprBits;

    unsigned IsNegative : 1;
  };
  enum { NumIntegerLiteralExprBits = NumLiteralExprBits + 1 };
  static_assert(NumIntegerLiteralExprBits <= 32, "fits in an unsigned");

  class AbstractClosureExprBitfields {
    friend class AbstractClosureExpr;
    unsigned : NumExprBits;
  };
  enum { NumAbstractClosureExprBits = NumExprBits + 0 };
  static_assert(NumAbstractClosureExprBits <= 32, "fits in an unsigned");

  class ClosureExprBitfields {
    friend class ClosureExpr;
    unsigned : NumAbstractClosureExprBits;

    /// True if closure parameters were synthesized from anonymous closure
    /// variables.
    unsigned HasAnonymousClosureVars : 1;
  };
  enum { NumClosureExprBits = NumAbstractClosureExprBits + 1 };
  static_assert(NumClosureExprBits <= 32, "fits in an unsigned");

protected:
  union {
    ExprBitfields ExprBits;
    LiteralExprBitfields LiteralExprBits;
    IntegerLiteralExprBitfields IntegerLiteralExprBits;
    AbstractClosureExprBitfields AbstractClosureExprBits;
    ClosureExprBitfields ClosureExprBits;
  };

private:
  /// Ty - This is the type of the expression.
  Type Ty;

protected:
  Expr(ExprKind Kind, bool Implicit, Type Ty = Type()) : Ty(Ty) {
    ExprBits.Kind = unsigned(Kind);
    ExprBits.Implicit = Implicit;
  }

public:
  /// Return the kind of this expression.
  ExprKind getKind() const { return ExprKind(ExprBits.Kind); }

  /// \brief Retrieve the name of the given expression kind.
  ///
  /// This name should only be used for debugging dumps and other
  /// developer aids, and should never be part of a diagnostic or exposed
  /// to the user of the compiler in any way.
  static StringRef getKindName(ExprKind K);

  /// getType - Return the type of this expression.
  Type getType() const { return Ty; }

  /// setType - Sets the type of this expression.
  void setType(Type T) { Ty = T; }

  /// \brief Return the source range of the expression.
  SourceRange getSourceRange() const;
  
  /// getStartLoc - Return the location of the start of the expression.
  SourceLoc getStartLoc() const { return getSourceRange().Start; }

  /// \brief Retrieve the location of the end of the expression.
  SourceLoc getEndLoc() const { return getSourceRange().End; }
  
  /// getLoc - Return the caret location of this expression.
  SourceLoc getLoc() const;

  SourceLoc TrailingSemiLoc;

  /// getSemanticsProvidingExpr - Find the smallest subexpression
  /// which obeys the property that evaluating it is exactly
  /// equivalent to evaluating this expression.
  ///
  /// Looks through parentheses.  Would not look through something
  /// like '(foo(), x:bar(), baz()).x'.
  Expr *getSemanticsProvidingExpr();

  /// getValueProvidingExpr - Find the smallest subexpression which is
  /// responsible for generating the value of this expression.
  /// Evaluating the result is not necessarily equivalent to
  /// evaluating this expression because of potential missing
  /// side-effects (which may influence the returned value).
  Expr *getValueProvidingExpr();

  /// walk - This recursively walks the AST rooted at this expression.
  Expr *walk(ASTWalker &walker);
  Expr *walk(ASTWalker &&walker) { return walk(walker); }
  
  /// isImplicit - Determines whether this expression was implicitly-generated,
  /// rather than explicitly written in the AST.
  bool isImplicit() const {
    return ExprBits.Implicit;
  }
  void setImplicit(bool Implicit = true) {
    ExprBits.Implicit = Implicit;
  }
  
  LLVM_ATTRIBUTE_DEPRECATED(
      void dump() const LLVM_ATTRIBUTE_USED,
      "only for use within the debugger");
  void dump(raw_ostream &OS) const;
  void print(raw_ostream &OS, unsigned Indent = 0) const;

  // Only allow allocation of Exprs using the allocator in ASTContext
  // or by doing a placement new.
  void *operator new(size_t Bytes, ASTContext &C,
                     unsigned Alignment = alignof(Expr));

  // Make placement new and vanilla new/delete illegal for Exprs.
  void *operator new(size_t Bytes) throw() = delete;
  void operator delete(void *Data) throw() = delete;
  void *operator new(size_t Bytes, void *Mem) throw() = delete;
};

/// ErrorExpr - Represents a semantically erroneous subexpression in the AST,
/// typically this will have an ErrorType.
class ErrorExpr : public Expr {
  SourceRange Range;
public:
  ErrorExpr(SourceRange Range, Type Ty = Type())
    : Expr(ExprKind::Error, /*Implicit=*/true, Ty), Range(Range) {}

  SourceRange getSourceRange() const { return Range; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Error;
  }
};

/// LiteralExpr - Common base class between the literals.
class LiteralExpr : public Expr {
public:
  LiteralExpr(ExprKind Kind, bool Implicit) : Expr(Kind, Implicit) {}
  
  
  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_LiteralExpr &&
           E->getKind() <= ExprKind::Last_LiteralExpr;
  }
};

/// \brief Integer literal with a '+' or '-' sign, like '+4' or '- 2'.
///
/// After semantic analysis assigns types, this is guaranteed to only have
/// a BuiltinIntegerType.
class IntegerLiteralExpr : public LiteralExpr {
  /// The value of the literal as an ASTContext-owned string. Underscores must
  /// be stripped.
  StringRef Val;  // Use StringRef instead of APInt, APInt leaks.
  SourceLoc MinusLoc;
  SourceLoc DigitsLoc;

public:
  IntegerLiteralExpr(StringRef Val, SourceLoc DigitsLoc, bool Implicit)
      : LiteralExpr(ExprKind::IntegerLiteral, Implicit), Val(Val),
        DigitsLoc(DigitsLoc) {
    IntegerLiteralExprBits.IsNegative = false;
  }

  APInt getValue() const;

  static APInt getValue(StringRef Text, unsigned BitWidth);

  bool isNegative() const { return IntegerLiteralExprBits.IsNegative; }
  void setNegative(SourceLoc Loc) {
    MinusLoc = Loc;
    IntegerLiteralExprBits.IsNegative = true;
  }

  StringRef getDigitsText() const { return Val; }

  SourceRange getSourceRange() const {
    if (isNegative())
      return { MinusLoc, DigitsLoc };
    else
      return DigitsLoc;
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::IntegerLiteral;
  }
};

/// FloatLiteralExpr - Floating point literal, like '4.0'.  After semantic
/// analysis assigns types, this is guaranteed to only have a
/// BuiltinFloatingPointType.
class FloatLiteralExpr : public LiteralExpr {
  /// The value of the literal as an ASTContext-owned string. Underscores must
  /// be stripped.
  StringRef Val; // Use StringRef instead of APFloat, APFloat leaks.
  SourceLoc Loc;

public:
  FloatLiteralExpr(StringRef Val, SourceLoc Loc, bool Implicit)
    : LiteralExpr(ExprKind::FloatLiteral, Implicit), Val(Val), Loc(Loc) {}

  APFloat getValue() const;
  
  static APFloat getValue(StringRef Text, const llvm::fltSemantics &Semantics);

  StringRef getText() const { return Val; }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::FloatLiteral;
  }
};

  
/// CharacterLiteral - Character literal, like 'x'.  After semantic analysis
/// assigns types, this is guaranteed to only have a 32-bit BuiltinIntegerType.
class CharacterLiteralExpr : public LiteralExpr {
  uint32_t Val;
  SourceLoc Loc;
public:
  CharacterLiteralExpr(uint32_t Val, SourceLoc Loc)
    : LiteralExpr(ExprKind::CharacterLiteral, /*Implicit=*/false),
      Val(Val), Loc(Loc) {}
  
  uint32_t getValue() const { return Val; }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::CharacterLiteral;
  }
};
  
/// StringLiteralExpr - String literal, like '"foo"'.  After semantic
/// analysis assigns types, this is guaranteed to only have a
/// BuiltinRawPointerType.
class StringLiteralExpr : public LiteralExpr {
  StringRef Val;
  SourceRange Range;
  
public:
  StringLiteralExpr(StringRef Val, SourceRange Range)
    : LiteralExpr(ExprKind::StringLiteral, /*Implicit=*/false),
      Val(Val), Range(Range) {}
  
  StringRef getValue() const { return Val; }
  SourceRange getSourceRange() const { return Range; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::StringLiteral;
  }
};

/// InterpolatedStringLiteral - An interpolated string literal.
///
/// An interpolated string literal mixes expressions (which are evaluated and
/// converted into string form) within a string literal.
///
/// \code
/// "[\(min)..\(max)]"
/// \endcode
class InterpolatedStringLiteralExpr : public LiteralExpr {
  SourceLoc Loc;
  MutableArrayRef<Expr *> Segments;
  Expr *SemanticExpr;
  
public:
  InterpolatedStringLiteralExpr(SourceLoc Loc, MutableArrayRef<Expr *> Segments)
    : LiteralExpr(ExprKind::InterpolatedStringLiteral, /*Implicit=*/false),
      Loc(Loc), Segments(Segments), SemanticExpr() { }
  
  MutableArrayRef<Expr *> getSegments() { return Segments; }
  ArrayRef<Expr *> getSegments() const { return Segments; }
  
  /// \brief Retrieve the expression that actually evaluates the resulting
  /// string, typically with a series of '+' operations.
  Expr *getSemanticExpr() const { return SemanticExpr; }
  void setSemanticExpr(Expr *SE) { SemanticExpr = SE; }
  
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::InterpolatedStringLiteral;
  }
};
  
/// MagicIdentifierLiteralExpr - A magic identifier like __FILE__ which expands
/// out to a literal at SILGen time.
class MagicIdentifierLiteralExpr : public LiteralExpr {
public:
  enum KindTy {
    File, Line, Column
  };
private:
  KindTy Kind;
  SourceLoc Loc;
  
public:
  MagicIdentifierLiteralExpr(KindTy Kind, SourceLoc Loc, bool Implicit)
    : LiteralExpr(ExprKind::MagicIdentifierLiteral, Implicit), Kind(Kind), Loc(Loc) {}
  
  KindTy getKind() const { return Kind; }
  bool isFile() const { return Kind == File; }
  bool isLine() const { return Kind == Line; }
  bool isColumn() const { return Kind == Column; }
  
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MagicIdentifierLiteral;
  }
};

/// DiscardAssignmentExpr - A '_' in the left-hand side of an assignment, which
/// discards the corresponding tuple element on the right-hand side.
class DiscardAssignmentExpr : public Expr {
  SourceLoc Loc;

public:
  DiscardAssignmentExpr(SourceLoc Loc, bool Implicit)
    : Expr(ExprKind::DiscardAssignment, Implicit), Loc(Loc) {}
  
  SourceRange getSourceRange() const { return Loc; }
  SourceLoc getLoc() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DiscardAssignment;
  }
};

/// DeclRefExpr - A reference to a value, "x".
class DeclRefExpr : public Expr {
  /// This is used when the reference is specialized, e.g "GenCls<Int>", to
  /// hold information about the generic arguments.
  struct SpecializeInfo {
    ConcreteDeclRef D;
    MutableArrayRef<TypeRepr*> GenericArgs;
  };

  /// \brief The declaration pointer or SpecializeInfo pointer if it was
  /// explicitly specialized with <...>.
  llvm::PointerUnion<ConcreteDeclRef, SpecializeInfo *> DOrSpecialized;
  SourceLoc Loc;

  SpecializeInfo *getSpecInfo() const {
    return DOrSpecialized.dyn_cast<SpecializeInfo*>();
  }

public:
  DeclRefExpr(ConcreteDeclRef D, SourceLoc Loc, bool Implicit, Type Ty = Type())
    : Expr(ExprKind::DeclRef, Implicit, Ty), DOrSpecialized(D), Loc(Loc) {}

  /// Retrieve the declaration to which this expression refers.
  ValueDecl *getDecl() const {
    return getDeclRef().getDecl();
  }

  /// Retrieve the concrete declaration reference.
  ConcreteDeclRef getDeclRef() const {
    if (auto Spec = getSpecInfo())
      return Spec->D;
    return DOrSpecialized.get<ConcreteDeclRef>();
  }

  /// Set the declaration.
  void setDeclRef(ConcreteDeclRef ref);

  void setSpecialized();

  /// \brief Determine whether this declaration reference was immediately
  /// specialized by <...>.
  bool isSpecialized() const { return getSpecInfo() != nullptr; }

  /// Set the generic arguments.
  ///
  /// This copies the array using ASTContext's allocator.
  void setGenericArgs(ArrayRef<TypeRepr*> GenericArgs);

  /// Returns the generic arguments if it was specialized or an empty array
  /// otherwise.
  ArrayRef<TypeRepr *> getGenericArgs() const {
    return const_cast<DeclRefExpr*>(this)->getGenericArgs();
  }
  MutableArrayRef<TypeRepr *> getGenericArgs() {
    if (auto Spec = getSpecInfo())
      return Spec->GenericArgs;
    return MutableArrayRef<TypeRepr *>();
  }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DeclRef;
  }
};
  
/// A reference to 'super'. References to members of 'super' resolve to members
/// of a superclass of 'self'.
class SuperRefExpr : public Expr {
  ValueDecl *Self;
  SourceLoc Loc;
  
public:
  SuperRefExpr(ValueDecl *Self, SourceLoc Loc, bool Implicit,
               Type SuperTy = Type())
    : Expr(ExprKind::SuperRef, Implicit, SuperTy), Self(Self), Loc(Loc) {}
  
  ValueDecl *getSelf() const { return Self; }
  
  SourceLoc getSuperLoc() const { return Loc; }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::SuperRef;
  }
};
  
/// A reference to another constructor from within a constructor body,
/// either to a delegating constructor or to a super.constructor invocation.
/// For a reference type, this semantically references a different constructor
/// entry point, called the 'initializing constructor', from the 'allocating
/// constructor' entry point referenced by a 'new' expression.
class OtherConstructorDeclRefExpr : public Expr {
  ConcreteDeclRef Ctor;
  SourceLoc Loc;
  
public:
  OtherConstructorDeclRefExpr(ConcreteDeclRef Ctor, SourceLoc Loc, Type Ty = {})
    : Expr(ExprKind::OtherConstructorDeclRef, /*Implicit=*/true, Ty),
      Ctor(Ctor), Loc(Loc)
  {}
  
  ConstructorDecl *getDecl() const;
  ConcreteDeclRef getDeclRef() const { return Ctor; }

  SourceLoc getConstructorLoc() const { return Loc; }
  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OtherConstructorDeclRef;
  }
};
  
/// An unresolved reference to a constructor member of a value. Resolves to a
/// DotSyntaxCall involving the value and the resolved constructor.
class UnresolvedConstructorExpr : public Expr {
  Expr *SubExpr;
  SourceLoc DotLoc;
  SourceLoc ConstructorLoc;
public:
  UnresolvedConstructorExpr(Expr *SubExpr, SourceLoc DotLoc,
                            SourceLoc ConstructorLoc, bool Implicit)
    : Expr(ExprKind::UnresolvedConstructor, Implicit),
      SubExpr(SubExpr), DotLoc(DotLoc), ConstructorLoc(ConstructorLoc)
  {}
  
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }
  
  SourceLoc getLoc() const { return ConstructorLoc; }
  SourceLoc getConstructorLoc() const { return ConstructorLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }
  
  SourceRange getSourceRange() const {
    return SourceRange(SubExpr->getStartLoc(), ConstructorLoc);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedConstructor;
  }
};

/// OverloadSetRefExpr - A reference to an overloaded set of values with a
/// single name.
///
/// This is an abstract class that covers the various different kinds of
/// overload sets.
class OverloadSetRefExpr : public Expr {
  ArrayRef<ValueDecl*> Decls;

protected:
  OverloadSetRefExpr(ExprKind Kind, ArrayRef<ValueDecl*> decls, bool Implicit,
                     Type Ty)
    : Expr(Kind, Implicit, Ty), Decls(decls) {}

public:
  ArrayRef<ValueDecl*> getDecls() const { return Decls; }
  
  /// getBaseType - Determine the type of the base object provided for the
  /// given overload set, which is only non-null when dealing with an overloaded
  /// member reference.
  Type getBaseType() const;

  /// hasBaseObject - Determine whether this overloaded expression has a
  /// concrete base object (which is not a metatype).
  bool hasBaseObject() const;

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_OverloadSetRefExpr &&
           E->getKind() <= ExprKind::Last_OverloadSetRefExpr;
  }
};

/// OverloadedDeclRefExpr - A reference to an overloaded name that should
/// eventually be resolved (by overload resolution) to a value reference.
class OverloadedDeclRefExpr : public OverloadSetRefExpr {
  SourceLoc Loc;
  bool IsSpecialized = false;

public:
  OverloadedDeclRefExpr(ArrayRef<ValueDecl*> Decls, SourceLoc Loc,
                        bool Implicit, Type Ty = Type())
    : OverloadSetRefExpr(ExprKind::OverloadedDeclRef, Decls, Implicit, Ty),
      Loc(Loc) { }
  
  SourceLoc getLoc() const { return Loc; }
  SourceRange getSourceRange() const { return Loc; }

  void setSpecialized(bool specialized) { IsSpecialized = specialized; }

  /// \brief Determine whether this declaration reference was immediately
  /// specialized by <...>.
  bool isSpecialized() const { return IsSpecialized; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OverloadedDeclRef;
  }
};

/// OverloadedMemberRefExpr - A reference to an overloaded name that is a
/// member, relative to some base expression, that will eventually be
/// resolved to some kind of member-reference expression.
class OverloadedMemberRefExpr : public OverloadSetRefExpr {
  Expr *SubExpr;
  SourceLoc DotLoc;
  SourceLoc MemberLoc;
  
public:
  OverloadedMemberRefExpr(Expr *SubExpr, SourceLoc DotLoc,
                          ArrayRef<ValueDecl *> Decls, SourceLoc MemberLoc,
                          bool Implicit, Type Ty = Type())
    : OverloadSetRefExpr(ExprKind::OverloadedMemberRef, Decls, Implicit, Ty),
      SubExpr(SubExpr), DotLoc(DotLoc), MemberLoc(MemberLoc) { }

  SourceLoc getDotLoc() const { return DotLoc; }
  SourceLoc getMemberLoc() const { return MemberLoc; }
  Expr *getBase() const { return SubExpr; }
  void setBase(Expr *E) { SubExpr = E; }
  
  SourceLoc getLoc() const { return MemberLoc; }
  SourceLoc getStartLoc() const {
    return DotLoc.isValid()? SubExpr->getStartLoc() : MemberLoc;
  }
  SourceLoc getEndLoc() const { return MemberLoc; }
  SourceRange getSourceRange() const {
    return SourceRange(getStartLoc(), MemberLoc);
  }

  static bool classof(const Expr *E) {
  return E->getKind() == ExprKind::OverloadedMemberRef;
  }
};
  
/// UnresolvedDeclRefExpr - This represents use of an undeclared identifier,
/// which may ultimately be a use of something that hasn't been defined yet, it
/// may be a use of something that got imported (which will be resolved during
/// sema), or may just be a use of an unknown identifier.
///
class UnresolvedDeclRefExpr : public Expr {
  Identifier Name;
  SourceLoc Loc;
  DeclRefKind RefKind;
  bool IsSpecialized = false;

public:
  UnresolvedDeclRefExpr(Identifier name, DeclRefKind refKind, SourceLoc loc)
    : Expr(ExprKind::UnresolvedDeclRef, /*Implicit=*/false), Name(name), Loc(loc),
      RefKind(refKind) {
  }
  
  Identifier getName() const { return Name; }
  DeclRefKind getRefKind() const { return RefKind; }

  void setSpecialized(bool specialized) { IsSpecialized = specialized; }

  /// \brief Determine whether this declaration reference was immediately
  /// specialized by <...>.
  bool isSpecialized() const { return IsSpecialized; }

  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedDeclRef;
  }
};
  
/// MemberRefExpr - This represents 'a.b' where we are referring to a member
/// of a type, such as a property or variable.
///
/// Note that methods found via 'dot' syntax are expressed as DotSyntaxCallExpr
/// nodes, because 'a.f' is actually an application of 'a' (the implicit object
/// argument) to the function 'f'.
class MemberRefExpr : public Expr {
  Expr *Base;
  ConcreteDeclRef Member;
  SourceLoc DotLoc;
  SourceLoc NameLoc;
  
public:  
  MemberRefExpr(Expr *base, SourceLoc dotLoc, ConcreteDeclRef member,
                SourceLoc nameLoc, bool Implicit);
  Expr *getBase() const { return Base; }
  ConcreteDeclRef getMember() const { return Member; }
  SourceLoc getNameLoc() const { return NameLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }
  
  void setBase(Expr *E) { Base = E; }
  
  SourceLoc getLoc() const { return NameLoc; }
  SourceRange getSourceRange() const {
    if (Base->isImplicit())
      return SourceRange(NameLoc);
  
    return SourceRange(Base->getStartLoc(), NameLoc);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MemberRef;
  }
};
  
/// ExistentialMemberRefExpr - This represents 'a.b' where we are referring to
/// a member of an existential type (e.g., a protocol member).
///
/// \code
/// protocol Printable {
///   func print(format : Format)
/// }
///
/// var p : Printable
/// p.print // An ExistentialMemberRefExpr with type (format : Format) -> ()
/// \endcode
class ExistentialMemberRefExpr : public Expr {
  Expr *Base;
  ConcreteDeclRef Value;
  SourceLoc DotLoc;
  SourceLoc NameLoc;
  
public:  
  ExistentialMemberRefExpr(Expr *Base, SourceLoc DotLoc, ConcreteDeclRef Value,
                           SourceLoc NameLoc);
  Expr *getBase() const { return Base; }
  ValueDecl *getDecl() const { return Value.getDecl(); }
  ConcreteDeclRef getDeclRef() const { return Value; }
  SourceLoc getNameLoc() const { return NameLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }
  
  void setBase(Expr *E) { Base = E; }
  
  SourceLoc getLoc() const { return NameLoc; }
  SourceRange getSourceRange() const {
    if (Base->isImplicit())
      return SourceRange(NameLoc);
    
    return SourceRange(Base->getStartLoc(), NameLoc);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ExistentialMemberRef;
  }
};

/// ArchetypeMemberRefExpr - This represents 'a.b' where we are referring to
/// a member of an archetype type (e.g., within a generic function).
///
/// \code
/// protocol Printable {
///   func print(format : Format)
/// }
///
/// func doPrint<P : Printable>(p : P) {
///   p.print(Format());
/// }
/// \endcode
class ArchetypeMemberRefExpr : public Expr {
  Expr *Base;
  ConcreteDeclRef Value;
  SourceLoc DotLoc;
  SourceLoc NameLoc;
  
public:  
  ArchetypeMemberRefExpr(Expr *Base, SourceLoc DotLoc, ConcreteDeclRef Value,
                         SourceLoc NameLoc);
  Expr *getBase() const { return Base; }
  ValueDecl *getDecl() const { return Value.getDecl(); }
  ConcreteDeclRef getDeclRef() const { return Value; }
  SourceLoc getNameLoc() const { return NameLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }
  
  void setBase(Expr *E) { Base = E; }
  
  SourceLoc getLoc() const { return NameLoc; }
  SourceRange getSourceRange() const {
    if (Base->isImplicit())
      return SourceRange(NameLoc);
    
    return SourceRange(Base->getStartLoc(), NameLoc);
  }

  /// getArchetype - Retrieve the archetype whose member is being accessed.
  ArchetypeType *getArchetype() const;

  /// isBaseIgnored - Determine whether the base expression is actually ignored,
  /// rather than being used as, e.g.,  the 'self' argument passed to an
  /// instance method or the base of a variable access.
  bool isBaseIgnored() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ArchetypeMemberRef;
  }
};

/// Common base for expressions that involve dynamic lookup, which
/// determines at runtime whether a particular method, property, or
/// subscript is available.
class DynamicLookupExpr : public Expr {
protected:
  explicit DynamicLookupExpr(ExprKind kind) : Expr(kind, /*Implicit=*/false) { }

public:
  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_DynamicLookupExpr &&
           E->getKind() <= ExprKind::Last_DynamicLookupExpr;
  }
};

/// A reference to a member of an object that was found via dynamic lookup.
///
/// A member found via dynamic lookup may not actually be available at runtime.
/// Therefore, a reference to that member always returns an optional instance.
/// Users can then propagate the optional (via ?) or assert that the member is
/// always available (via !). For example:
///
/// \code
/// class C {
///   func [objc] foo(i : Int) -> String { ... }
/// };
///
/// var x : DynamicLookup = <some value>
/// print(x.foo!(17)) // x.foo has type ((i : Int) -> String)?
/// \endcode
class DynamicMemberRefExpr : public DynamicLookupExpr {
  Expr *Base;
  ConcreteDeclRef Member;
  SourceLoc DotLoc;
  SourceLoc NameLoc;

public:
  DynamicMemberRefExpr(Expr *base, SourceLoc dotLoc,
                       ConcreteDeclRef member,
                       SourceLoc nameLoc)
    : DynamicLookupExpr(ExprKind::DynamicMemberRef),
      Base(base), Member(member), DotLoc(dotLoc), NameLoc(nameLoc) {
    }

  /// Retrieve the base of the expression.
  Expr *getBase() const { return Base; }

  /// Replace the base of the expression.
  void setBase(Expr *base) { Base = base; }

  /// Retrieve the member to which this access refers.
  ConcreteDeclRef getMember() const { return Member; }

  /// Retrieve the location of the member name.
  SourceLoc getNameLoc() const { return NameLoc; }

  /// Retrieve the location of the '.'.
  SourceLoc getDotLoc() const { return DotLoc; }

  SourceLoc getLoc() const { return NameLoc; }

  SourceRange getSourceRange() const {
    if (Base->isImplicit())
      return SourceRange(NameLoc);

    return SourceRange(Base->getStartLoc(), NameLoc);
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DynamicMemberRef;
  }
};

/// A subscript on an object with dynamic lookup type.
///
/// A subscript found via dynamic lookup may not actually be available
/// at runtime.  Therefore, the result of performing the subscript
/// operation always returns an optional instance.Users can then
/// propagate the optional (via ?) or assert that the member is always
/// available (via !). For example:
///
/// \code
/// class C {
///   subscript [objc] (i : Int) -> String { 
///   get: 
///     ... 
///   }
/// };
///
/// var x : DynamicLookup = <some value>
/// print(x[27]! // x[27] has type String?
/// \endcode
class DynamicSubscriptExpr : public DynamicLookupExpr {
  Expr *Base;
  Expr *Index;
  ConcreteDeclRef Member;

public:
  DynamicSubscriptExpr(Expr *base, Expr *index, 
                       ConcreteDeclRef member)
    : DynamicLookupExpr(ExprKind::DynamicSubscript),
      Base(base), Index(index), Member(member) { }

  /// Retrieve the base of the expression.
  Expr *getBase() const { return Base; }

  /// Replace the base of the expression.
  void setBase(Expr *base) { Base = base; }

  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }

  /// Retrieve the member to which this access refers.
  ConcreteDeclRef getMember() const { return Member; }

  SourceLoc getLoc() const { return Index->getStartLoc(); }

  SourceRange getSourceRange() const {
    return SourceRange(Base->getStartLoc(), Index->getEndLoc());
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DynamicSubscript;
  }
};

/// UnresolvedMemberExpr - This represents '.foo', an unresolved reference to a
/// member, which is to be resolved with context sensitive type information into
/// bar.foo.  These always have unresolved type.
class UnresolvedMemberExpr : public Expr {
  SourceLoc DotLoc;
  SourceLoc NameLoc;
  Identifier Name;

public:  
  UnresolvedMemberExpr(SourceLoc dotLoc, SourceLoc nameLoc,
                       Identifier name)
    : Expr(ExprKind::UnresolvedMember, /*Implicit=*/false),
      DotLoc(dotLoc), NameLoc(nameLoc), Name(name) {
  }

  Identifier getName() const { return Name; }
  SourceLoc getNameLoc() const { return NameLoc; }
  SourceLoc getDotLoc() const { return DotLoc; }

  SourceLoc getLoc() const { return NameLoc; }
  SourceRange getSourceRange() const { 
    return SourceRange(DotLoc, NameLoc);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedMember;
  }
};
  
/// ParenExpr - A parenthesized expression like '(x+x)'.  Syntactically,
/// this is just a TupleExpr with exactly one element that has no label.
/// Semantically, however, it serves only as grouping parentheses and
/// does not form an expression of tuple type (unless the sub-expression
/// has tuple type, of course).
class ParenExpr : public Expr {
  SourceLoc LParenLoc, RParenLoc;
  Expr *SubExpr;

  /// \brief Whether we're wrapping a trailing closure expression.
  /// FIXME: Pack bit into superclass.
  bool HasTrailingClosure;

  // FIXME: Hack for CollectionExpr::getElements()
  friend class CollectionExpr;

public:
  ParenExpr(SourceLoc lploc, Expr *subExpr, SourceLoc rploc,
            bool hasTrailingClosure,
            Type ty = Type())
    : Expr(ExprKind::Paren, /*Implicit=*/false, ty),
      LParenLoc(lploc), RParenLoc(rploc),
      SubExpr(subExpr), HasTrailingClosure(hasTrailingClosure) {
    assert(lploc.isValid() == rploc.isValid() &&
           "Mismatched source location information");
  }

  SourceLoc getLParenLoc() const { return LParenLoc; }
  SourceLoc getRParenLoc() const { return RParenLoc; }

  SourceLoc getLoc() const { return SubExpr->getLoc(); }
  SourceRange getSourceRange() const {
    // When the locations of the parentheses are invalid, ask our subexpression
    // for its source range instead.
    if (LParenLoc.isInvalid())
      return SubExpr->getSourceRange();

    // If we have a trailing closure, our end point is the end of the trailing
    // closure.
    if (HasTrailingClosure)
      return SourceRange(LParenLoc, SubExpr->getEndLoc());

    return SourceRange(LParenLoc, RParenLoc);
  }

  /// \brief Whether this expression has a trailing closure as its argument.
  bool hasTrailingClosure() const { return HasTrailingClosure; }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *E) { SubExpr = E; }

  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Paren; }
};
  
/// TupleExpr - Parenthesized expressions like '(a: x+x)' and '(x, y, 4)'.  Also
/// used to represent the operands to a binary operator.  Note that
/// expressions like '(4)' are represented with a ParenExpr.
class TupleExpr : public Expr {
  SourceLoc LParenLoc;
  SourceLoc RParenLoc;
  /// SubExprs - Elements of these can be set to null to get the default init
  /// value for the tuple element.
  MutableArrayRef<Expr *> SubExprs;
  /// SubExprNames - Can be null if no names.  Otherwise length = SubExpr.size()
  Identifier *SubExprNames;

  /// \brief Whether we're wrapping a trailing closure expression.
  /// FIXME: Pack bit into superclass.
  bool HasTrailingClosure;

public:
  TupleExpr(SourceLoc LParenLoc, MutableArrayRef<Expr *> SubExprs,
            Identifier *SubExprNames, SourceLoc RParenLoc,
            bool hasTrailingClosure, bool Implicit, Type Ty = Type())
    : Expr(ExprKind::Tuple, Implicit, Ty),
      LParenLoc(LParenLoc), RParenLoc(RParenLoc),
      SubExprs(SubExprs), SubExprNames(SubExprNames),
      HasTrailingClosure(hasTrailingClosure)
  {
    assert(LParenLoc.isValid() == RParenLoc.isValid() &&
           "Mismatched parenthesis location information validity");
  }

  SourceLoc getLParenLoc() const { return LParenLoc; }
  SourceLoc getRParenLoc() const { return RParenLoc; }

  SourceRange getSourceRange() const;

  /// \brief Whether this expression has a trailing closure as its argument.
  bool hasTrailingClosure() const { return HasTrailingClosure; }

  MutableArrayRef<Expr*> getElements() {
    return SubExprs;
  }

  ArrayRef<Expr*> getElements() const {
    return SubExprs;
  }
  
  unsigned getNumElements() const { return SubExprs.size(); }
  
  Expr *getElement(unsigned i) const {
    return SubExprs[i];
  }
  void setElement(unsigned i, Expr *e) {
    SubExprs[i] = e;
  }

  bool hasElementNames() const { return SubExprNames; }

  Identifier *getElementNames() const { return SubExprNames; }
  
  Identifier getElementName(unsigned i) const {
    return SubExprNames ? SubExprNames[i] : Identifier();
  }
  
  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Tuple; }
};

/// \brief A collection literal expression.
///
/// The subexpression is represented as a TupleExpr or ParenExpr and
/// passed on to the appropriate semantics-providing conversion
/// operation.
class CollectionExpr : public Expr {
  SourceLoc LBracketLoc;
  SourceLoc RBracketLoc;
  Expr *SubExpr;
  Expr *SemanticExpr;

protected:
  CollectionExpr(ExprKind Kind, SourceLoc LBracketLoc, Expr *SubExpr, 
                 SourceLoc RBracketLoc, Type Ty)
    : Expr(Kind, /*Implicit=*/false, Ty),
      LBracketLoc(LBracketLoc), RBracketLoc(RBracketLoc),
      SubExpr(SubExpr), SemanticExpr(nullptr) { }

public:
  /// Get the ParenExpr or TupleExpr representing the literal contents
  /// of the container.
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }

  /// Retrieve the elements stored in the collection.
  ArrayRef<Expr *> getElements() const;

  SourceLoc getLBracketLoc() const { return LBracketLoc; }
  SourceLoc getRBracketLoc() const { return RBracketLoc; }
  SourceRange getSourceRange() const {
    return SourceRange(LBracketLoc, RBracketLoc);
  }
  
  Expr *getSemanticExpr() const { return SemanticExpr; }
  void setSemanticExpr(Expr *e) { SemanticExpr = e; }

  static bool classof(const Expr *e) {
    return e->getKind() >= ExprKind::First_CollectionExpr &&
           e->getKind() <= ExprKind::Last_CollectionExpr;
  }

};
 
/// \brief An array literal expression [a, b, c].
class ArrayExpr : public CollectionExpr {
public:
  ArrayExpr(SourceLoc LBracketLoc, Expr *SubExpr, SourceLoc RBracketLoc,
            Type Ty = Type())
    : CollectionExpr(ExprKind::Array, LBracketLoc, SubExpr, RBracketLoc, Ty) { }
    
  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Array;
  }
};

/// \brief A dictionary literal expression [a : x, b : y, c : z].
class DictionaryExpr : public CollectionExpr {
public:
  DictionaryExpr(SourceLoc LBracketLoc, Expr *SubExpr, SourceLoc RBracketLoc,
                 Type Ty = Type())
    : CollectionExpr(ExprKind::Dictionary, LBracketLoc, SubExpr, RBracketLoc, 
                     Ty) { }
    
  static bool classof(const Expr *e) {
    return e->getKind() == ExprKind::Dictionary;
  }
};

/// Subscripting expressions like a[i] that refer to an element within a
/// container.
///
/// There is no built-in subscripting in the language. Rather, a fully
/// type-checked and well-formed subscript expression refers to a subscript
/// declaration, which provides a getter and (optionally) a setter that will
/// be used to perform reads/writes.
class SubscriptExpr : public Expr {
  ConcreteDeclRef TheDecl;
  Expr *Base;
  Expr *Index;
  
public:
  SubscriptExpr(Expr *base, Expr *index,
                ConcreteDeclRef decl = ConcreteDeclRef())
    : Expr(ExprKind::Subscript, /*Implicit=*/false, Type()),
      TheDecl(decl), Base(base), Index(index) { }
  
  /// getBase - Retrieve the base of the subscript expression, i.e., the
  /// value being indexed.
  Expr *getBase() const { return Base; }
  void setBase(Expr *E) { Base = E; }
  
  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }
  
  /// Determine whether subscript operation has a known underlying
  /// subscript declaration or not.
  bool hasDecl() const { return static_cast<bool>(TheDecl); }
  
  /// Retrieve the subscript declaration that this subscripting
  /// operation refers to. Only valid when \c hasDecl() is true.
  ConcreteDeclRef getDecl() const {
    assert(hasDecl() && "No subscript declaration known!");
    return TheDecl;
  }

  SourceRange getSourceRange() const {
    return SourceRange(Base->getStartLoc(), Index->getEndLoc());
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Subscript;
  }
};

/// ExistentialSubscriptExpr - Subscripting expressions like a[i] that refer to
/// an element within a container, where the container has existential type.
///
/// There is no built-in subscripting in the language. Rather, a fully
/// type-checked and well-formed subscript expression refers to a subscript
/// declaration, which provides a getter and (optionally) a setter that will
/// be used to perform reads/writes.
class ExistentialSubscriptExpr : public Expr {
  SubscriptDecl *D;
  Expr *Base;
  Expr *Index;
  
public:
  ExistentialSubscriptExpr(Expr *Base, Expr *Index, SubscriptDecl *D);
  
  /// getBase - Retrieve the base of the subscript expression, i.e., the
  /// value being indexed. This value has existential type.
  Expr *getBase() const { return Base; }
  void setBase(Expr *E) { Base = E; }
  
  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }
  
  /// getDecl - Retrieve the subscript declaration that this subscripting
  /// operation refers to. 
  SubscriptDecl *getDecl() const { return D; }

  SourceRange getSourceRange() const {
    return SourceRange(Base->getStartLoc(), Index->getEndLoc());
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ExistentialSubscript;
  }
};

/// ArchetypeSubscriptExpr - Subscripting expressions like a[i] that refer to
/// an element within a container, where the container is an archetype.
class ArchetypeSubscriptExpr : public Expr {
  SubscriptDecl *D;
  Expr *Base;
  Expr *Index;
  
public:
  ArchetypeSubscriptExpr(Expr *Base, Expr *Index, SubscriptDecl *D);
  
  /// getBase - Retrieve the base of the subscript expression, i.e., the
  /// value being indexed. This value has archetype type.
  Expr *getBase() const { return Base; }
  void setBase(Expr *E) { Base = E; }
  
  /// getIndex - Retrieve the index of the subscript expression, i.e., the
  /// "offset" into the base value.
  Expr *getIndex() const { return Index; }
  void setIndex(Expr *E) { Index = E; }
  
  /// getDecl - Retrieve the subscript declaration that this subscripting
  /// operation refers to. 
  SubscriptDecl *getDecl() const { return D; }

  SourceRange getSourceRange() const {
    return SourceRange(Base->getStartLoc(), Index->getEndLoc());
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ArchetypeSubscript;
  }
};

/// UnresolvedDotExpr - A member access (foo.bar) on an expression with
/// unresolved type.
class UnresolvedDotExpr : public Expr {
  Expr *SubExpr;
  SourceLoc DotLoc;
  SourceLoc NameLoc;
  Identifier Name;
public:
  UnresolvedDotExpr(Expr *subexpr, SourceLoc dotloc, Identifier name,
                    SourceLoc nameloc, bool Implicit)
  : Expr(ExprKind::UnresolvedDot, Implicit), SubExpr(subexpr), DotLoc(dotloc),
    NameLoc(nameloc), Name(name) {}
  
  SourceLoc getLoc() const { return NameLoc; }
  
  SourceRange getSourceRange() const {
    if (DotLoc.isInvalid())
      return SourceRange(NameLoc, NameLoc);
    return SourceRange(SubExpr->getStartLoc(), NameLoc);
  }
  
  SourceLoc getDotLoc() const { return DotLoc; }
  Expr *getBase() const { return SubExpr; }
  void setBase(Expr *e) { SubExpr = e; }

  Identifier getName() const { return Name; }
  SourceLoc getNameLoc() const { return NameLoc; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedDot;
  }
};

/// ModuleExpr - Reference a module by name.  The module being referenced is
/// captured in the type of the expression, which is always a ModuleType.
class ModuleExpr : public Expr {
  SourceLoc Loc;
  
public:
  ModuleExpr(SourceLoc Loc, Type Ty)
  : Expr(ExprKind::Module, /*Implicit=*/false, Ty), Loc(Loc) {}
  
  SourceRange getSourceRange() const { return SourceRange(Loc, Loc); }
  SourceLoc getLoc() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Module;
  }
};


/// TupleElementExpr - Refer to an element of a tuple,
/// e.g. "(1,field:2).field".
class TupleElementExpr : public Expr {
  Expr *SubExpr;
  SourceLoc NameLoc;
  unsigned FieldNo;
  SourceLoc DotLoc;

public:
  TupleElementExpr(Expr *SubExpr, SourceLoc DotLoc, unsigned FieldNo,
                   SourceLoc NameLoc, Type Ty)
    : Expr(ExprKind::TupleElement, /*Implicit=*/false, Ty), SubExpr(SubExpr),
      NameLoc(NameLoc), FieldNo(FieldNo), DotLoc(DotLoc) {}

  SourceLoc getLoc() const { return NameLoc; }
  Expr *getBase() const { return SubExpr; }
  void setBase(Expr *e) { SubExpr = e; }

  unsigned getFieldNumber() const { return FieldNo; }
  SourceLoc getNameLoc() const { return NameLoc; }  
  SourceLoc getDotLoc() const { return DotLoc; }
  
  SourceRange getSourceRange() const { 
    return SourceRange(getBase()->getStartLoc(), getNameLoc());
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::TupleElement;
  }
};

/// \brief Describes a monadic bind from T? to T.
///
/// In a ?-chain expression, this is the part that's spelled with a
/// postfix ?.
///
/// A BindOptionalExpr must always appear within a
/// OptionalEvaluationExpr.  If the operand of the BindOptionalExpr
/// evaluates to a missing value, the OptionalEvaluationExpr
/// immediately completes and produces a missing value in the result
/// type.
class BindOptionalExpr : public Expr {
  Expr *SubExpr;
  SourceLoc QuestionLoc;

public:
  BindOptionalExpr(Expr *subExpr, SourceLoc questionLoc, Type ty = Type())
    : Expr(ExprKind::BindOptional, /*Implicit=*/ false, ty),
      SubExpr(subExpr), QuestionLoc(questionLoc) {}

  SourceRange getSourceRange() const {
    return SourceRange(SubExpr->getStartLoc(), QuestionLoc);
  }
  SourceLoc getLoc() const { return getQuestionLoc(); }
  SourceLoc getQuestionLoc() const { return QuestionLoc; }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::BindOptional;
  }
};

/// \brief Describes the outer limits of an operation containing
/// monadic binds of T? to T.
///
/// In a ?-chain expression, this is implicitly formed at the outer
/// limits of the chain.  For example, in (foo?.bar?().baz).fred,
/// this is nested immediately within the parens.
///
/// This expression will always have optional type.
class OptionalEvaluationExpr : public Expr {
  Expr *SubExpr;

public:
  OptionalEvaluationExpr(Expr *subExpr, Type ty = Type())
    : Expr(ExprKind::OptionalEvaluation, /*Implicit=*/ true, ty),
      SubExpr(subExpr) {}

  SourceRange getSourceRange() const { return SubExpr->getSourceRange(); }
  SourceLoc getLoc() const { return SubExpr->getLoc(); }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OptionalEvaluation;
  }
};

/// \brief An expression that forces an optional to its underlying value.
///
/// \code
/// func parseInt(s : String) -> Int? { ... }
///
/// var maybeInt = parseInt("5"); // returns an Int?
/// var forcedInt = parseInt("5")!; // returns an Int; fails on empty optional
/// \endcode
///
class ForceValueExpr : public Expr {
  Expr *SubExpr;
  SourceLoc ExclaimLoc;

public:
  ForceValueExpr(Expr *subExpr, SourceLoc exclaimLoc)
    : Expr(ExprKind::ForceValue, /*Implicit=*/ false, Type()),
      SubExpr(subExpr), ExclaimLoc(exclaimLoc) {}

  SourceRange getSourceRange() const {
    return SourceRange(SubExpr->getStartLoc(), ExclaimLoc);
  }
  SourceLoc getLoc() const { return getExclaimLoc(); }
  SourceLoc getExclaimLoc() const { return ExclaimLoc; }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *expr) { SubExpr = expr; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ForceValue;
  }
};

/// ImplicitConversionExpr - An abstract class for expressions which
/// implicitly convert the value of an expression in some way.
class ImplicitConversionExpr : public Expr {
  Expr *SubExpr;

protected:
  ImplicitConversionExpr(ExprKind kind, Expr *subExpr, Type ty)
    : Expr(kind, /*Implicit=*/true, ty), SubExpr(subExpr) {}

public:
  SourceRange getSourceRange() const { return SubExpr->getSourceRange(); }
  SourceLoc getLoc() const { return SubExpr->getLoc(); }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_ImplicitConversionExpr &&
           E->getKind() <= ExprKind::Last_ImplicitConversionExpr;
  }
};

/// InjectIntoOptionalExpr - The implicit conversion from T to T?.
class InjectIntoOptionalExpr : public ImplicitConversionExpr {
public:
  InjectIntoOptionalExpr(Expr *subExpr, Type ty)
    : ImplicitConversionExpr(ExprKind::InjectIntoOptional, subExpr, ty) {}

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::InjectIntoOptional;
  }
};
  
/// BridgeToBlockExpr - FIXME: A hack to represent limited Swift closure to
/// ObjC block conversion.
class BridgeToBlockExpr : public ImplicitConversionExpr {
public:
  BridgeToBlockExpr(Expr *subExpr, Type ty)
    : ImplicitConversionExpr(ExprKind::BridgeToBlock, subExpr, ty) {}
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::BridgeToBlock;
  }
};

/// TupleShuffleExpr - This represents a permutation of a tuple value to a new
/// tuple type.  The expression's type is known to be a tuple type and the
/// subexpression is known to have a tuple type as well.
class TupleShuffleExpr : public ImplicitConversionExpr {
public:
  enum : int {
    /// The element mapping value indicating that a field of the destination
    /// tuple should be default-initialized.
    DefaultInitialize = -1,
    /// The element mapping value signaling the first variadic field.
    FirstVariadic = -2,
    /// The element mapping value indicating that the field of the
    /// destination tuple should be default-initialized with an expression
    /// provided by the caller.
    /// FIXME: Yet another indication that TupleShuffleExpr uses the wrong
    /// formulation.
    CallerDefaultInitialize = -3
  };
private:
  /// This contains an entry for each element in the Expr type.  Each element
  /// specifies which index from the SubExpr that the destination element gets.
  /// If the element value is DefaultInitialize, then the destination value
  /// gets the default initializer for that tuple element value.
  ArrayRef<int> ElementMapping;

  /// If we're doing a varargs shuffle, this is the function to build the
  /// destination slice type.
  Expr *InjectionFn;

  /// If there are any default arguments, the owning function
  /// declaration.
  ValueDecl *DefaultArgsOwner;

  ArrayRef<Expr *> CallerDefaultArgs;

public:
  TupleShuffleExpr(Expr *subExpr, ArrayRef<int> elementMapping, 
                   ValueDecl *defaultArgsOwner,
                   ArrayRef<Expr *> CallerDefaultArgs, Type ty)
    : ImplicitConversionExpr(ExprKind::TupleShuffle, subExpr, ty),
      ElementMapping(elementMapping), InjectionFn(nullptr),
      DefaultArgsOwner(defaultArgsOwner), CallerDefaultArgs(CallerDefaultArgs)
  {
  }

  ArrayRef<int> getElementMapping() const { return ElementMapping; }

  /// Set the injection function expression to use.
  void setVarargsInjectionFunction(Expr *fn) { InjectionFn = fn; }
  Expr *getVarargsInjectionFunction() const {
    assert(InjectionFn != nullptr);
    return InjectionFn;
  }
  Expr *getVarargsInjectionFunctionOrNull() const {
    return InjectionFn;
  }

  /// Retrieve the owner of the default arguments.
  ValueDecl *getDefaultArgsOwner() const { return DefaultArgsOwner; }

  /// Retrieve the caller-defaulted arguments.
  ArrayRef<Expr *> getCallerDefaultArgs() const { return CallerDefaultArgs; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::TupleShuffle;
  }
};

/// LoadExpr - Turn an l-value into an r-value by performing a "load"
/// operation.  This operation may actually be a logical operation,
/// i.e. one implemented using a call to a potentially user-defined
/// function instead of a simple memory transaction.
class LoadExpr : public ImplicitConversionExpr {
public:
  LoadExpr(Expr *subExpr, Type type)
    : ImplicitConversionExpr(ExprKind::Load, subExpr, type) {}

  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Load; }
};

/// MaterializeExpr - Turn an r-value into an l-value by placing it in
/// temporary memory.
class MaterializeExpr : public ImplicitConversionExpr {
public:
  MaterializeExpr(Expr *subExpr, Type ty)
    : ImplicitConversionExpr(ExprKind::Materialize, subExpr, ty) {}

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Materialize;
  }
};

/// RequalifyExpr - Change the qualification on an l-value.  The new
/// type always has the same object type as the old type with strictly
/// "more" (i.e. a supertyped set of) qualifiers.
class RequalifyExpr : public ImplicitConversionExpr {
  bool IsForObject;
public:
  RequalifyExpr(Expr *subExpr, Type type, bool isForObject = false)
    : ImplicitConversionExpr(ExprKind::Requalify, subExpr, type),
      IsForObject(isForObject) {}

  /// Is this requalification for the object operand?
  ///
  /// Qualification adjustments for the object operand are permitted
  /// to remove non-settability.  This is neither sound nor a good
  /// idea, but it's necessary until we have the capacity to control
  /// mutation.
  bool isForObjectOperand() const { return IsForObject; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Requalify;
  }
};
  
/// FunctionConversionExpr - Convert a function to another function type,
/// which might involve renaming the parameters or handling substitutions
/// of subtypes (in the return) or supertypes (in the input).
///
/// FIXME: This should be a CapturingExpr.
class FunctionConversionExpr : public ImplicitConversionExpr {
public:
  FunctionConversionExpr(Expr *subExpr, Type type)
    : ImplicitConversionExpr(ExprKind::FunctionConversion, subExpr, type) {}
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::FunctionConversion;
  }
};

/// MetatypeConversionExpr - Convert a metatype to another metatype
/// using essentially a derived-to-base conversion.
class MetatypeConversionExpr : public ImplicitConversionExpr {
public:
  MetatypeConversionExpr(Expr *subExpr, Type type)
    : ImplicitConversionExpr(ExprKind::MetatypeConversion, subExpr, type) {}
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::MetatypeConversion;
  }
};

/// ErasureExpr - Perform type erasure by converting a value to existential
/// type. For example:
///
/// \code
/// protocol Printable {
///   func print()
/// }
///
/// struct Book {
///   func print() { ... }
/// }
///
/// var printable : Printable = Book() // erases type
/// \endcode
class ErasureExpr : public ImplicitConversionExpr {
  ArrayRef<ProtocolConformance *> Conformances;
  
public:
  ErasureExpr(Expr *SubExpr, Type Ty,
              ArrayRef<ProtocolConformance *> Conformances)
    : ImplicitConversionExpr(ExprKind::Erasure, SubExpr, Ty),
      Conformances(Conformances) {}
  
  /// \brief Retrieve the mapping specifying how the type of the subexpression
  /// maps to the resulting existential type. If the resulting existential
  /// type involves several different protocols, there will be mappings for each
  /// of those protocols, in the order in which the existential type expands
  /// its properties.
  ///
  /// The entries in this array may be null, indicating that the conformance
  /// to the corresponding protocol is trivial (because the source
  /// type is either an archetype or an existential type that conforms to
  /// that corresponding protocol).
  ArrayRef<ProtocolConformance *> getConformances() const {
    return Conformances;
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Erasure;
  }
};

/// UnresolvedSpecializeExpr - Represents an explicit specialization using
/// a type parameter list (e.g. "Vector<Int>") that has not been resolved.
class UnresolvedSpecializeExpr : public Expr {
  Expr *SubExpr;
  SourceLoc LAngleLoc;
  SourceLoc RAngleLoc;
  MutableArrayRef<TypeLoc> UnresolvedParams;
public:
  UnresolvedSpecializeExpr(Expr *SubExpr,
                           SourceLoc LAngleLoc,
                           MutableArrayRef<TypeLoc> UnresolvedParams,
                           SourceLoc RAngleLoc)
    : Expr(ExprKind::UnresolvedSpecialize, /*Implicit=*/false),
      SubExpr(SubExpr),
      LAngleLoc(LAngleLoc), RAngleLoc(RAngleLoc),
      UnresolvedParams(UnresolvedParams) { }
  
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }
  
  /// \brief Retrieve the list of type parameters. These parameters have not yet
  /// been bound to archetypes of the entity to be specialized.
  ArrayRef<TypeLoc> getUnresolvedParams() const { return UnresolvedParams; }
  MutableArrayRef<TypeLoc> getUnresolvedParams() { return UnresolvedParams; }
  
  SourceLoc getLoc() const { return LAngleLoc; }
  SourceLoc getLAngleLoc() const { return LAngleLoc; }
  SourceLoc getRAngleLoc() const { return RAngleLoc; }
  SourceRange getSourceRange() const {
    return SourceRange(SubExpr->getStartLoc(), RAngleLoc);
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedSpecialize;
  }
};

/// \brief Describes an implicit conversion from a subclass to one of its
/// superclasses.
class DerivedToBaseExpr : public ImplicitConversionExpr {
public:
  DerivedToBaseExpr(Expr *subExpr, Type type)
    : ImplicitConversionExpr(ExprKind::DerivedToBase, subExpr, type) {}

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DerivedToBase;
  }
};

/// \brief Describes an implicit conversion from a value of archetype type to
/// its concrete superclass.
class ArchetypeToSuperExpr : public ImplicitConversionExpr {
public:
  ArchetypeToSuperExpr(Expr *subExpr, Type type)
    : ImplicitConversionExpr(ExprKind::ArchetypeToSuper, subExpr, type) {}

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ArchetypeToSuper;
  }
};

/// ScalarToTupleExpr - Convert a scalar to tuple type.
class ScalarToTupleExpr : public ImplicitConversionExpr {
public:
  /// Describes an element of the destination tuple, which can be the
  /// caller-side default argument expression, the declaration from which the
  /// callee-side default argument should be produced, or null to indicate the
  /// 'hole' where the scalar expression should be placed.
  typedef llvm::PointerUnion<Expr *, ValueDecl *> Element;

private:
  /// If we're doing a varargs shuffle, this is the function to build the
  /// destination slice type.
  Expr *InjectionFn;

  /// The elements of the destination tuple.
  MutableArrayRef<Element> Elements;

public:
  ScalarToTupleExpr(Expr *subExpr, Type type,
                    MutableArrayRef<Element> elements,
                    Expr *InjectionFn = nullptr)
    : ImplicitConversionExpr(ExprKind::ScalarToTuple, subExpr, type),
      InjectionFn(InjectionFn), Elements(elements) {}

  /// Retrieve the index of the scalar field within the destination tuple.
  unsigned getScalarField() const;

  /// Retrieve the expression that refers to the injection function.
  Expr *getVarargsInjectionFunction() { return InjectionFn; }

  /// Retrieve the elements of the destination tuple.
  MutableArrayRef<Element> getElements() { return Elements; }
  ArrayRef<Element> getElements() const { return Elements; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ScalarToTuple;
  }
};

/// AddressOfExpr - Using the builtin unary '&' operator, convert the
/// given l-value into an explicit l-value.
class AddressOfExpr : public Expr {
  Expr *SubExpr;
  SourceLoc OperLoc;

public:
  AddressOfExpr(SourceLoc operLoc, Expr *subExpr, Type type)
    : Expr(ExprKind::AddressOf, /*Implicit=*/false, type),
      SubExpr(subExpr), OperLoc(operLoc) {}

  SourceRange getSourceRange() const {
    return SourceRange(OperLoc, SubExpr->getEndLoc());
  }
  SourceLoc getLoc() const { return OperLoc; }

  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *e) { SubExpr = e; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::AddressOf;
  }
};

/// SequenceExpr - A list of binary operations which has not yet been
/// folded into a tree.  The operands all have even indices, while the
/// subexpressions with odd indices are all (potentially overloaded)
/// references to binary operators.
class SequenceExpr : public Expr {
  unsigned NumElements;

  Expr **getSubExprs() { return reinterpret_cast<Expr **>(this + 1); }
  Expr * const *getSubExprs() const {
    return const_cast<SequenceExpr*>(this)->getSubExprs();
  }

  SequenceExpr(ArrayRef<Expr*> elements)
    : Expr(ExprKind::Sequence, /*Implicit=*/false),
      NumElements(elements.size()) {
    assert(NumElements > 0 && "zero-length sequence!");
    memcpy(getSubExprs(), elements.data(), elements.size() * sizeof(Expr*));
  }

public:
  static SequenceExpr *create(ASTContext &ctx, ArrayRef<Expr*> elements);

  SourceRange getSourceRange() const { 
    return SourceRange(getElements()[0]->getStartLoc(),
                       getElements()[getNumElements() - 1]->getEndLoc());
  }
  
  unsigned getNumElements() const { return NumElements; }

  MutableArrayRef<Expr*> getElements() {
    return MutableArrayRef<Expr*>(getSubExprs(), NumElements);
  }

  ArrayRef<Expr*> getElements() const {
    return ArrayRef<Expr*>(getSubExprs(), NumElements);
  }

  Expr *getElement(unsigned i) const {
    assert(i < NumElements);
    return getSubExprs()[i];
  }
  void setElement(unsigned i, Expr *e) {
    assert(i < NumElements);
    getSubExprs()[i] = e;
  }

  // Implement isa/cast/dyncast/etc.
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Sequence;
  }
};

/// \brief A base class for closure expressions.
class AbstractClosureExpr : public Expr, public DeclContext {
  CaptureInfo Captures;

  /// \brief The set of parameters.
  Pattern *ParamPattern;

public:
  AbstractClosureExpr(ExprKind Kind, Type FnType, bool Implicit,
                      DeclContext *Parent)
      : Expr(Kind, Implicit, FnType),
        DeclContext(DeclContextKind::AbstractClosureExpr, Parent),
        ParamPattern(nullptr)
  {}

  CaptureInfo &getCaptureInfo() { return Captures; }
  const CaptureInfo &getCaptureInfo() const { return Captures; }

  /// \brief Retrieve the parameters of this closure.
  Pattern *getParams() { return ParamPattern; }
  const Pattern *getParams() const { return ParamPattern; }
  void setParams(Pattern *P) { ParamPattern = P; }

  ArrayRef<Pattern *> getParamPatterns() { return ParamPattern; }
  ArrayRef<const Pattern *> getParamPatterns() const { return ParamPattern; }

  /// \brief Retrieve the result type of this closure.
  Type getResultType() const;

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_AbstractClosureExpr &&
           E->getKind() <= ExprKind::Last_AbstractClosureExpr;
  }

  static bool classof(const DeclContext *DC) {
    return DC->getContextKind() == DeclContextKind::AbstractClosureExpr;
  }

  using DeclContext::operator new;
};

/// \brief An explicit unnamed function expression, which can optionally have
/// named arguments.
///
/// \code
///     { $0 + $1 }
///     { a, b -> Int in a + b }
///     { (a : Int, b : Int) -> Int in a + b }
/// \endcode
class ClosureExpr : public AbstractClosureExpr {
  /// \brief The location of the '->' denoting an explicit return type,
  /// if present.
  SourceLoc arrowLoc;

  /// \brief The explicitly-specified result type.
  TypeLoc explicitResultType;

  /// \brief The body of the closure, along with a bit indicating whether it
  /// was originally just a single expression.
  llvm::PointerIntPair<BraceStmt *, 1, bool> body;
  
public:
  ClosureExpr(Pattern *Params, SourceLoc arrowLoc,
              TypeLoc explicitResultType, DeclContext *Parent)
    : AbstractClosureExpr(ExprKind::Closure, Type(), /*Implicit=*/false, Parent),
      arrowLoc(arrowLoc), explicitResultType(explicitResultType),
      body(nullptr) {
    setParams(Params);
    ClosureExprBits.HasAnonymousClosureVars = false;
  }

  SourceRange getSourceRange() const;
  SourceLoc getLoc() const;

  BraceStmt *getBody() const { return body.getPointer(); }
  void setBody(BraceStmt *S, bool isSingleExpression) {
    body.setPointer(S);
    body.setInt(isSingleExpression);
  }

  /// \brief Determine whether the parameters of this closure are actually
  /// anonymous closure variables.
  bool hasAnonymousClosureVars() const {
    return ClosureExprBits.HasAnonymousClosureVars;
  }

  /// \brief Set the parameters of this closure along with a flag indicating
  /// whether these parameters are actually anonymous closure variables.
  void setHasAnonymousClosureVars() {
    ClosureExprBits.HasAnonymousClosureVars = true;
  }

  /// \brief Determine whether this closure expression has an
  /// explicitly-specified result type.
  bool hasExplicitResultType() const { return arrowLoc.isValid(); }

  /// \brief Retrieve the location of the \c '->' for closures with an
  /// explicit result type.
  SourceLoc getArrowLoc() const {
    assert(hasExplicitResultType() && "No arrow location");
    return arrowLoc;
  }

  /// \brief Retrieve the explicit result type location information.
  TypeLoc &getExplicitResultTypeLoc() {
    assert(hasExplicitResultType() && "No explicit result type");
    return explicitResultType;
  }

  /// \brief Determine whether the closure has a single expression for its
  /// body.
  ///
  /// This will be true for closures such as, e.g.,
  /// \code
  ///   { $0 + 1 }
  /// \endcode
  ///
  /// or
  ///
  /// \code
  ///   { x, y in x > y }
  /// \endcode
  ///
  /// But not for empty closures nor 
  bool hasSingleExpressionBody() const {
    return body.getInt();
  }

  /// \brief Retrieve the body for closure that has a single expression for
  /// its body.
  ///
  /// Only valid when \c hasSingleExpressionBody() is true.
  Expr *getSingleExpressionBody() const;

  /// \brief Set the body for a closure that has a single expression as its
  /// body.
  ///
  /// This routine cannot change whether a closure has a single expression as
  /// its body; it can only update that expression.
  void setSingleExpressionBody(Expr *NewBody);

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Closure;
  }
};

/// \brief This is a closure of the contained subexpression that is formed
/// when an scalar expression is converted to [auto_closure] function type.
/// For example:
/// \code
///   var x : [auto_closure] () -> int = 4
/// \endcode
class AutoClosureExpr : public AbstractClosureExpr {
  BraceStmt *Body;

public:
  AutoClosureExpr(Expr *Body, Type ResultTy, DeclContext *Parent)
      : AbstractClosureExpr(ExprKind::AutoClosure, ResultTy, /*Implicit=*/true,
                            Parent) {
    setBody(Body);
  }

  SourceRange getSourceRange() const;

  BraceStmt *getBody() const { return Body; }
  void setBody(Expr *E);

  /// Returns the body of the auto_closure as an \c Expr.
  ///
  /// The body of an auto_closure always consists of a single expression.
  Expr *getSingleExpressionBody() const;

  // Implement isa/cast/dyncast/etc.
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::AutoClosure;
  }
};

/// The allocation of an array.  Allocates and constructs
/// the array, then injects that into the corresponding slice type.
class NewArrayExpr : public Expr {
public:
  struct Bound {
    Expr *Value;
    SourceRange Brackets;

    Bound() = default;
    Bound(Expr *value, SourceRange brackets)
      : Value(value), Brackets(brackets) {}
  };

private:
  TypeLoc ElementTyAsWritten;
  Type ElementTy;
  unsigned NumBounds;
  SourceLoc NewLoc;
  Expr *InjectionFn;
  Expr *ConstructionFn;

  NewArrayExpr(SourceLoc newLoc, TypeLoc elementTy,
               unsigned numBounds,
               Expr *constructionFn)
    : Expr(ExprKind::NewArray, /*Implicit=*/false, Type()),
      ElementTyAsWritten(elementTy),
      NumBounds(numBounds), NewLoc(newLoc),
      InjectionFn(nullptr), ConstructionFn(constructionFn) {}

  Bound *getBoundsBuffer() {
    return reinterpret_cast<Bound*>(this + 1);
  }
  const Bound *getBoundsBuffer() const {
    return reinterpret_cast<const Bound*>(this + 1);
  }

public:
  static NewArrayExpr *create(ASTContext &Context, SourceLoc newLoc,
                              TypeLoc elementTy, ArrayRef<Bound> bounds,
                              Expr *constructionFn);

  unsigned getNumBounds() const { return NumBounds; }

  MutableArrayRef<Bound> getBounds() {
    return MutableArrayRef<Bound>(getBoundsBuffer(), getNumBounds());
  }
  ArrayRef<Bound> getBounds() const {
    return ArrayRef<Bound>(getBoundsBuffer(), getNumBounds());
  }

  /// Return the location of the 'new' keyword.
  SourceLoc getNewLoc() const { return NewLoc; }

  SourceRange getSourceRange() const {
    auto endLoc = ConstructionFn && !ConstructionFn->isImplicit()
      ? ConstructionFn->getEndLoc()
      : getBounds().back().Brackets.End;
    return SourceRange(NewLoc, endLoc);
  }
  SourceLoc getLoc() const { return NewLoc; }

  /// Set the injection function expression to use to form the array value.
  void setInjectionFunction(Expr *fn) { InjectionFn = fn; }
  Expr *getInjectionFunction() const {
    assert(InjectionFn != nullptr);
    return InjectionFn;
  }
  
  bool hasInjectionFunction() const { return InjectionFn != nullptr; }

  /// Set the construction function expression to use to initialize the array
  /// elements. This should have function type (IndexType) -> ElementType.
  void setConstructionFunction(Expr *fn) { ConstructionFn = fn; }
  Expr *getConstructionFunction() const {
    assert(ConstructionFn != nullptr);
    return ConstructionFn;
  }
  
  bool hasConstructionFunction() const { return ConstructionFn != nullptr; }
  
  bool hasElementType() const { return !ElementTy.isNull(); }

  Type getElementType() const {
    assert(ElementTy && "Element type not yet computed!");
    return ElementTy;
  }
  void setElementType(Type T) { ElementTy = T; }
  TypeLoc &getElementTypeLoc() { return ElementTyAsWritten; }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::NewArray;
  }
};
  
/// MetatypeExpr - Produces a metatype value.
///
/// The metatype value can come either from a evaluating an expression (then
/// getting its metatype) or from a type that was parsed in the source. If
/// neither is available, this isn't a parsed form.
class MetatypeExpr : public Expr {
  llvm::PointerUnion<Expr *, TypeRepr *> BaseOrType;
  SourceLoc MetatypeLoc;

public:
  explicit MetatypeExpr(Expr *base, SourceLoc metatypeLoc, Type ty)
    : Expr(ExprKind::Metatype, /*Implicit=*/true, ty),
      BaseOrType(base), MetatypeLoc(metatypeLoc) { }

  explicit MetatypeExpr(TypeRepr *tyRepr)
    : Expr(ExprKind::Metatype, /*Implicit=*/false, Type()),
      BaseOrType(tyRepr) { }

  Expr *getBase() const {
    return BaseOrType.dyn_cast<Expr *>();
  }
  void setBase(Expr *base) { BaseOrType = base; }

  TypeRepr *getBaseTypeRepr() const {
    return BaseOrType.dyn_cast<TypeRepr *>();
  }

  void setBaseTypeErpr(TypeRepr *tyR) { BaseOrType = tyR; }

  SourceLoc getLoc() const;

  SourceRange getSourceRange() const;

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Metatype;
  }
};

/// An expression referring to an opaque object of a fixed type.
///
/// Opaque value expressions occur when a particular value within the AST
/// needs to be re-used without being re-evaluated or for a value that is
/// a placeholder. OpaqueValueExpr nodes are introduced by some other AST
/// node (say, a \c DynamicMemberRefExpr) and can only be used within the
/// subexpressions of that AST node.
class OpaqueValueExpr : public Expr {
  SourceLoc Loc;
  bool UniquelyReferenced = false;

public:
  explicit OpaqueValueExpr(SourceLoc Loc, Type Ty)
    : Expr(ExprKind::OpaqueValue, /*Implicit=*/true, Ty), Loc(Loc) { }

  /// Determine whether this opaque value is referenced at only one point in
  /// the AST.
  ///
  /// Opaque values referenced at only one place in the AST can be referenced
  /// more efficiently, be eliminating extra retain/release traffic.
  bool isUniquelyReferenced() const { return UniquelyReferenced; }

  void setUniquelyReferenced(bool uniqueRef) { UniquelyReferenced = uniqueRef; }

  SourceRange getSourceRange() const { return Loc; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::OpaqueValue; 
  }
};

/// ApplyExpr - Superclass of various function calls, which apply an argument to
/// a function to get a result.
class ApplyExpr : public Expr {
  /// The function being called.
  Expr *Fn;

  /// The argument being passed to it, and whether it's a 'super' argument.
  llvm::PointerIntPair<Expr *, 1, bool> ArgAndIsSuper;

protected:
  ApplyExpr(ExprKind Kind, Expr *Fn, Expr *Arg, bool Implicit, Type Ty = Type())
    : Expr(Kind, Implicit, Ty), Fn(Fn), ArgAndIsSuper(Arg, false) {
    assert(classof((Expr*)this) && "ApplyExpr::classof out of date");
  }

public:
  Expr *getFn() const { return Fn; }
  void setFn(Expr *e) { Fn = e; }

  Expr *getArg() const { return ArgAndIsSuper.getPointer(); }
  void setArg(Expr *e) {
    assert((getKind() != ExprKind::Binary || isa<TupleExpr>(e)) &&
           "BinaryExprs must have a TupleExpr as the argument");
    ArgAndIsSuper = {e, ArgAndIsSuper.getInt()};
  }
  
  bool isSuper() const { return ArgAndIsSuper.getInt(); }
  void setIsSuper(bool super) {
    ArgAndIsSuper = {ArgAndIsSuper.getPointer(), super};
  }

  ValueDecl *getCalledValue() const;

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_ApplyExpr &&
           E->getKind() <= ExprKind::Last_ApplyExpr;
  }
};
  
/// CallExpr - Application of an argument to a function, which occurs
/// syntactically through juxtaposition with a TupleExpr whose
/// leading '(' is unspaced.
class CallExpr : public ApplyExpr {
public:
  CallExpr(Expr *fn, Expr *arg, bool Implicit, Type ty = Type())
    : ApplyExpr(ExprKind::Call, fn, arg, Implicit, ty) {}

  SourceRange getSourceRange() const {
    return SourceRange(getFn()->getStartLoc(), getArg()->getEndLoc()); 
  }
  
  SourceLoc getLoc() const { return getFn()->getLoc(); }
  
  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Call; }
};
  
/// PrefixUnaryExpr - Prefix unary expressions like '!y'.
class PrefixUnaryExpr : public ApplyExpr {
public:
  PrefixUnaryExpr(Expr *Fn, Expr *Arg, Type Ty = Type())
    : ApplyExpr(ExprKind::PrefixUnary, Fn, Arg, /*Implicit=*/false, Ty) {}

  SourceLoc getLoc() const { return getFn()->getStartLoc(); }

  SourceRange getSourceRange() const {
    return SourceRange(getFn()->getStartLoc(), getArg()->getEndLoc()); 
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::PrefixUnary;
  }
};

/// PostfixUnaryExpr - Prefix unary expressions like '!y'.
class PostfixUnaryExpr : public ApplyExpr {
public:
  PostfixUnaryExpr(Expr *Fn, Expr *Arg, Type Ty = Type())
    : ApplyExpr(ExprKind::PostfixUnary, Fn, Arg, /*Implicit=*/false, Ty) {}

  SourceLoc getLoc() const { return getFn()->getStartLoc(); }
  
  SourceRange getSourceRange() const {
    return SourceRange(getArg()->getStartLoc(), getFn()->getEndLoc()); 
  }  

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::PostfixUnary;
  }
};
  
/// BinaryExpr - Infix binary expressions like 'x+y'.  The argument is always
/// an implicit tuple expression of the type expected by the function.
class BinaryExpr : public ApplyExpr {
public:
  BinaryExpr(Expr *Fn, TupleExpr *Arg, bool Implicit, Type Ty = Type())
    : ApplyExpr(ExprKind::Binary, Fn, Arg, Implicit, Ty) {}

  SourceLoc getLoc() const { return getFn()->getLoc(); }

  SourceRange getSourceRange() const {
    return getArg()->getSourceRange();
  }  

  TupleExpr *getArg() const { return cast<TupleExpr>(ApplyExpr::getArg()); }

  static bool classof(const Expr *E) { return E->getKind() == ExprKind::Binary;}
};

/// SelfApplyExpr - Abstract application that provides the 'self' pointer for
/// a method curried as (this : Self) -> (params) -> result.
///
/// The application of a curried method to 'self' semantically differs from
/// normal function application because the 'self' parameter can be implicitly
/// materialized from an rvalue.
class SelfApplyExpr : public ApplyExpr {
protected:
  SelfApplyExpr(ExprKind K, Expr *FnExpr, Expr *BaseExpr, Type Ty)
    : ApplyExpr(K, FnExpr, BaseExpr, FnExpr->isImplicit(), Ty) { }
  
public:
  Expr *getBase() const { return getArg(); }
  void setBase(Expr *E) { setArg(E); }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_SelfApplyExpr &&
           E->getKind() <= ExprKind::Last_SelfApplyExpr;
  }
};

/// DotSyntaxCallExpr - Refer to a method of a type, e.g. P.x.  'x'
/// is modeled as a DeclRefExpr or OverloadSetRefExpr on the method.
class DotSyntaxCallExpr : public SelfApplyExpr {
  SourceLoc DotLoc;
  
public:
  DotSyntaxCallExpr(Expr *FnExpr, SourceLoc DotLoc, Expr *BaseExpr,
                    Type Ty = Type())
    : SelfApplyExpr(ExprKind::DotSyntaxCall, FnExpr, BaseExpr, Ty),
      DotLoc(DotLoc) {
    setImplicit(DotLoc.isInvalid());
  }

  SourceLoc getDotLoc() const { return DotLoc; }

  SourceLoc getLoc() const {
    return isImplicit() ? getBase()->getStartLoc() : getFn()->getLoc();
  }
  SourceLoc getStartLoc() const {
    return getBase()->getStartLoc();
  }
  SourceLoc getEndLoc() const {
    return isImplicit() ? getBase()->getEndLoc() : getFn()->getEndLoc();
  }
  SourceRange getSourceRange() const {
    return SourceRange(getStartLoc(), getEndLoc());
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DotSyntaxCall;
  }
};

/// ConstructorRefCallExpr - Refer to a constructor for a type P.  The
/// actual reference to function which returns the constructor is modeled
/// as a DeclRefExpr.
class ConstructorRefCallExpr : public SelfApplyExpr {
public:
  ConstructorRefCallExpr(Expr *FnExpr, Expr *BaseExpr, Type Ty = Type())
    : SelfApplyExpr(ExprKind::ConstructorRefCall, FnExpr, BaseExpr, Ty) {}

  SourceLoc getLoc() const { return getFn()->getLoc(); }
  SourceLoc getStartLoc() const { return getBase()->getStartLoc(); }
  SourceLoc getEndLoc() const { return getFn()->getEndLoc(); }
  SourceRange getSourceRange() const {
    return SourceRange(getStartLoc(), getEndLoc());
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ConstructorRefCall;
  }
};

/// DotSyntaxBaseIgnoredExpr - When a.b resolves to something that does not need
/// the actual value of the base (e.g. when applied to a metatype, module, or
/// the base of a 'static' function) this expression node is created.  The
/// semantics are that its base is evaluated and discarded, then 'b' is
/// evaluated and returned as the result of the expression.
class DotSyntaxBaseIgnoredExpr : public Expr {
  Expr *LHS;
  SourceLoc DotLoc;
  Expr *RHS;
public:
  DotSyntaxBaseIgnoredExpr(Expr *LHS, SourceLoc DotLoc, Expr *RHS)
    : Expr(ExprKind::DotSyntaxBaseIgnored, /*Implicit=*/false, RHS->getType()),
      LHS(LHS), DotLoc(DotLoc), RHS(RHS) {
  }
  
  Expr *getLHS() { return LHS; }
  void setLHS(Expr *E) { LHS = E; }
  SourceLoc getDotLoc() const { return DotLoc; }
  Expr *getRHS() { return RHS; }
  void setRHS(Expr *E) { RHS = E; }

  SourceLoc getStartLoc() const {
    return DotLoc.isValid()? LHS->getStartLoc() : RHS->getStartLoc();
  }
  
  SourceRange getSourceRange() const {
    return SourceRange(getStartLoc(), RHS->getEndLoc());
  }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DotSyntaxBaseIgnored;
  }
};

/// \brief Represents an explicit cast, 'a as T' or 'a is T', where "T" is a
/// type, and "a" is the expression that will be converted to the type.
class ExplicitCastExpr : public Expr {
  Expr *SubExpr;
  SourceLoc AsLoc;
  TypeLoc CastTy;

protected:
  ExplicitCastExpr(ExprKind kind, Expr *sub, SourceLoc AsLoc, TypeLoc castTy,
                   Type resultTy)
    : Expr(kind, /*Implicit=*/false), SubExpr(sub), AsLoc(AsLoc), CastTy(castTy)
  {}

public:
  Expr *getSubExpr() const { return SubExpr; }
  
  /// Get the type syntactically spelled in the cast. For some forms of checked
  /// cast this is different from the result type of the expression.
  TypeLoc &getCastTypeLoc() { return CastTy; }

  /// Get the type syntactically spelled in the cast. For some forms of checked
  /// cast this is different from the result type of the expression.
  TypeLoc getCastTypeLoc() const { return CastTy; }

  void setSubExpr(Expr *E) { SubExpr = E; }

  SourceLoc getLoc() const {
    if (AsLoc.isValid())
      return AsLoc;

    return SubExpr->getLoc();
  }

  SourceRange getSourceRange() const {
    if (CastTy.getSourceRange().isInvalid())
      return SubExpr->getSourceRange();

    return SubExpr
      ? SourceRange{SubExpr->getStartLoc(), CastTy.getSourceRange().End}
      : SourceRange{AsLoc, CastTy.getSourceRange().End};
  }
  
  /// True if the node has been processed by SequenceExpr folding.
  bool isFolded() const { return SubExpr; }

  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_ExplicitCastExpr &&
           E->getKind() <= ExprKind::Last_ExplicitCastExpr;
  }
};

/// Discriminates the different kinds of checked cast supported.
enum class CheckedCastKind {
  /// The kind has not been determined yet.
  Unresolved,
  /// The requested conversion is implicit and should be represented as a
  /// coercion.
  InvalidCoercible,
  
  /// Valid resolved kinds start here.
  First_Resolved,
  
  /// A cast from a class to one of its subclasses.
  Downcast = First_Resolved,
  /// A cast from a class to a type parameter constrained by that class as a
  /// superclass.
  SuperToArchetype,
  /// A cast from a type parameter to another type parameter.
  ArchetypeToArchetype,
  /// A cast from a type parameter to a concrete type.
  ArchetypeToConcrete,
  /// A cast from an existential type to a type parameter.
  ExistentialToArchetype,
  /// A cast from an existential type to a concrete type.
  ExistentialToConcrete,
  /// A cast from a concrete type to a type parameter.
  ConcreteToArchetype,
  /// A cast from a concrete type to an existential type it is not statically
  /// known to conform to.
  ConcreteToUnrelatedExistential,
};
  
/// \brief Abstract base class for checked casts 'as' and 'is'. These represent
/// casts that can dynamically fail.
class CheckedCastExpr : public ExplicitCastExpr {
  CheckedCastKind CastKind;
public:
  CheckedCastExpr(ExprKind kind,
                  Expr *sub, SourceLoc asLoc, TypeLoc castTy, Type resultTy)
    : ExplicitCastExpr(kind, sub, asLoc, castTy, resultTy),
      CastKind(CheckedCastKind::Unresolved)
  {}
  
  /// Return the semantic kind of cast performed.
  CheckedCastKind getCastKind() const { return CastKind; }
  void setCastKind(CheckedCastKind kind) { CastKind = kind; }
  
  /// True if the cast has been type-checked and its kind has been set.
  bool isResolved() const {
    return CastKind >= CheckedCastKind::First_Resolved;
  }
  
  static bool classof(const Expr *E) {
    return E->getKind() >= ExprKind::First_CheckedCastExpr
        && E->getKind() <= ExprKind::Last_CheckedCastExpr;
  }
};

/// \brief Represents an explicit conditional checked cast, which converts
/// from a type to some subtype and produces an Optional value, which will be
/// .Some(x) if the cast succeeds, or .None if the cast fails.
/// Spelled 'a as T' and produces a value of type 'T?'.
class ConditionalCheckedCastExpr : public CheckedCastExpr {
public:
  ConditionalCheckedCastExpr(Expr *sub, SourceLoc asLoc, TypeLoc type)
    : CheckedCastExpr(ExprKind::ConditionalCheckedCast,
                      sub, asLoc, type, type.getType())
  { }
  
  ConditionalCheckedCastExpr(SourceLoc asLoc, TypeLoc type)
    : ConditionalCheckedCastExpr(nullptr, asLoc, type)
  {}
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ConditionalCheckedCast;
  }
};

/// \brief Represents a runtime type check query, 'a is T', where 'T' is a type
/// and 'a' is a value of some related type. Evaluates to a Bool true if 'a' is
/// of the type and 'a as T' would succeed, false otherwise.
///
/// FIXME: We should support type queries with a runtime metatype value too.
class IsaExpr : public CheckedCastExpr {
public:
  IsaExpr(Expr *sub, SourceLoc isLoc, TypeLoc type)
    : CheckedCastExpr(ExprKind::Isa,
                      sub, isLoc, type, Type())
  {}
  
  IsaExpr(SourceLoc isLoc, TypeLoc type)
    : IsaExpr(nullptr, isLoc, type)
  {}
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Isa;
  }
};
  
/// \brief Represents the rebinding of 'self' in a constructor that calls out
/// to another constructor. The result of the subexpression is assigned to
/// 'self', and the expression returns void.
///
/// When a super.constructor or delegating constructor is invoked, 'self' is
/// reassigned to the result of the constructor (after being downcast in the
/// case of super.constructor).
/// This is needed for reference types with ObjC interop, where
/// reassigning 'self' is a supported feature, and for value type delegating
/// constructors, where the delegatee constructor is responsible for
/// initializing 'self' in-place before the delegator's logic executes.
class RebindSelfInConstructorExpr : public Expr {
  Expr *SubExpr;
  ValueDecl *Self;
public:
  RebindSelfInConstructorExpr(Expr *SubExpr, ValueDecl *Self);
  
  SourceLoc getLoc() const { return SubExpr->getLoc(); }
  SourceRange getSourceRange() const { return SubExpr->getSourceRange(); }
  
  ValueDecl *getSelf() const { return Self; }
  Expr *getSubExpr() const { return SubExpr; }
  void setSubExpr(Expr *Sub) { SubExpr = Sub; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::RebindSelfInConstructor;
  }
};
  
/// \brief The conditional expression 'x ? y : z'.
class IfExpr : public Expr {
  Expr *CondExpr, *ThenExpr, *ElseExpr;
  SourceLoc QuestionLoc, ColonLoc;
public:
  IfExpr(Expr *CondExpr,
         SourceLoc QuestionLoc, Expr *ThenExpr,
         SourceLoc ColonLoc, Expr *ElseExpr,
         Type Ty = Type())
    : Expr(ExprKind::If, /*Implicit=*/false, Ty),
      CondExpr(CondExpr), ThenExpr(ThenExpr), ElseExpr(ElseExpr),
      QuestionLoc(QuestionLoc), ColonLoc(ColonLoc)
  {}
  
  IfExpr(SourceLoc QuestionLoc, Expr *ThenExpr, SourceLoc ColonLoc)
    : IfExpr(nullptr, QuestionLoc, ThenExpr, ColonLoc, nullptr)
  {}
  
  SourceLoc getLoc() const { return QuestionLoc; }
  SourceRange getSourceRange() const {
    if (isFolded())
      return {CondExpr->getStartLoc(), ElseExpr->getEndLoc()};
    return {QuestionLoc, ColonLoc};
  }
  SourceLoc getQuestionLoc() const { return QuestionLoc; }
  SourceLoc getColonLoc() const { return ColonLoc; }
  
  Expr *getCondExpr() const { return CondExpr; }
  void setCondExpr(Expr *E) { CondExpr = E; }
  
  Expr *getThenExpr() const { return ThenExpr; }
  void setThenExpr(Expr *E) { ThenExpr = E; }
  
  Expr *getElseExpr() const { return ElseExpr; }
  void setElseExpr(Expr *E) { ElseExpr = E; }
  
  /// True if the node has been processed by binary expression folding.
  bool isFolded() const { return CondExpr && ElseExpr; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::If;
  }
};

/// AssignExpr - A value assignment, like "x = y".
class AssignExpr : public Expr {
  Expr *Dest;
  Expr *Src;
  SourceLoc EqualLoc;

public:  
  AssignExpr(Expr *Dest, SourceLoc EqualLoc, Expr *Src, bool Implicit)
    : Expr(ExprKind::Assign, Implicit),
      Dest(Dest), Src(Src), EqualLoc(EqualLoc) {}
  
  AssignExpr(SourceLoc EqualLoc)
    : AssignExpr(nullptr, EqualLoc, nullptr, /*Implicit=*/false)
  {}

  Expr *getDest() const { return Dest; }
  void setDest(Expr *e) { Dest = e; }
  Expr *getSrc() const { return Src; }
  void setSrc(Expr *e) { Src = e; }
  
  SourceLoc getEqualLoc() const { return EqualLoc; }
  
  SourceLoc getLoc() const { return EqualLoc; }
  SourceRange getSourceRange() const;
  
  /// True if the node has been processed by binary expression folding.
  bool isFolded() const { return Dest && Src; }
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::Assign;
  }
};
  
/// \brief An expression that produces a zero value for types that
/// default-initialize to zero, including builtin types and classes.
///
/// This expression is synthesizes by type checking and cannot be written
/// directly by the user.
class ZeroValueExpr : public Expr {
public:
  explicit ZeroValueExpr(Type Ty)
    : Expr(ExprKind::ZeroValue, /*Implicit=*/true, Ty) { }

  SourceRange getSourceRange() const { return SourceRange(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::ZeroValue;
  }
};

/// \brief An expression that describes the use of a default value, which may
/// come from the default argument of a function type or member initializer.
///
/// This expression is synthesized by type checking and cannot be written
/// directly by the user.
class DefaultValueExpr : public Expr {
  Expr *subExpr;

public:
  explicit DefaultValueExpr(Expr *subExpr)
    : Expr(ExprKind::DefaultValue, /*Implicit=*/true, subExpr->getType()),
      subExpr(subExpr) { }

  Expr *getSubExpr() const { return subExpr; }
  void setSubExpr(Expr *sub) { subExpr = sub; }
  
  SourceRange getSourceRange() const { return SourceRange(); }

  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::DefaultValue;
  }
};
  
/// \brief A pattern production that has been parsed but hasn't been resolved
/// into a complete pattern. Name binding converts these into standalone pattern
/// nodes or raises an error if a pattern production appears in an invalid
/// position.
class UnresolvedPatternExpr : public Expr {
  Pattern *subPattern;

public:
  explicit UnresolvedPatternExpr(Pattern *subPattern)
    : Expr(ExprKind::UnresolvedPattern, /*Implicit=*/false),
      subPattern(subPattern) { }
  
  const Pattern *getSubPattern() const { return subPattern; }
  Pattern *getSubPattern() { return subPattern; }
  void setSubPattern(Pattern *p) { subPattern = p; }
  
  SourceLoc getLoc() const;
  SourceRange getSourceRange() const;
  
  static bool classof(const Expr *E) {
    return E->getKind() == ExprKind::UnresolvedPattern;
  }
};
  
} // end namespace swift

#endif