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205 lines
8.4 KiB
ReStructuredText
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.. title:: Lexicon
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.. default-role:: term
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.. @raise litre.TestsAreMissing
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This file defines several terms used by the Swift compiler and standard library
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source code, tests, and commit messages. See also the `LLVM lexicon`_.
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.. _LLVM lexicon: http://llvm.org/docs/Lexicon.html
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.. note::
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This document uses Sphinx-specific features. If you are viewing this on
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GitHub, you'll have to use raw mode, or download and build the docs
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yourself.
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.. glossary::
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archetype
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A placeholder for a generic parameter or an associated type within a
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generic context.
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canonical SIL
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SIL after the
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`mandatory passes <mandatory passes / mandatory optimizations>` have run.
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This can be used as input to IRGen to generate LLVM IR or object files.
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Clang importer
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The part of the compiler that reads C and Objective-C declarations and
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exposes them as Swift. Essentially contains a small instance of Clang
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running inside the Swift compiler, which is also used during IRGen.
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conformance
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A construct detailing how a particular type conforms to a particular
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protocol. Represented in the compiler by the ProtocolConformance type at
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the AST level. See also `witness table`.
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DI (definite initialization / definitive initialization)
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The feature that no uninitialized variables, constants, or properties will
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be read by a program, or the analysis pass that operates on SIL to
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guarantee this. This was `discussed on Apple's Swift blog`__.
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__ https://developer.apple.com/swift/blog/?id=28
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existential
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A value whose type is a protocol composition (including a single protocol
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and *zero* protocols; the latter is the ``Any`` type).
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fragile
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Describes a type or function where making changes will break binary
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compatibility. See :doc:`LibraryEvolution.rst <LibraryEvolution>`.
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IUO (implicitly unwrapped optional)
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A type like Optional, but it implicitly converts to its wrapped type. If
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the value is ``nil`` during such a conversion, the program traps just as
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it would when a normal Optional is force-unwrapped. IUOs implicitly
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convert to and from normal Optionals with the same wrapped type.
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main module
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The module for the file or files currently being compiled.
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mandatory passes / mandatory optimizations
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Transformations over SIL that run immediately after SIL generation. Once
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all mandatory passes have run (and if no errors are found), the SIL is
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considered `canonical <canonical SIL>`.
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metatype
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The type of a value representing a type. Greg Parker has a good
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explanation of `Objective-C's "metaclasses"`__; because Swift has types
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that are *not* classes, a more general term is used.
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We also sometimes refer to a value representing a type as a "metatype
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object" or just "metatype", usually within low-level contexts like IRGen
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and LLDB. This is technically incorrect (it's just a "type object"), but
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the malapropism happened early in the project and has stuck around.
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__ http://sealiesoftware.com/blog/archive/2009/04/14/objc_explain_Classes_and_metaclasses.html
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model
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A type that conforms to a particular protocol. Sometimes "concrete
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model". Example: "Array and Set are both models of CollectionType".
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module
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Has *many* uses in the Swift world. We may want to rename some of them.
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#1 and #2 are the most common.
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1. A unit of API distribution and grouping. The ``import`` declaration
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brings modules into scope. Represented as ModuleDecl in the compiler.
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2. A compilation unit; that is, source files that are compiled together.
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These files may contain cross-references. Represented as "the main
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module" (a specific ModuleDecl).
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3. (as "SIL module") A container for SIL to be compiled together, along
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with various context for the compilation.
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4. (as "LLVM module") A collection of LLVM IR to be compiled together.
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Always created in an LLVMContext.
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5. A file containing serialized AST and SIL information for a source file
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or entire compilation unit. Often "swiftmodule file", with "swiftmodule"
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pronounced as a single word.
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6. (as "Clang module") A set of self-contained C-family header files.
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Represented by a ClangModuleUnit in the Swift compiler, each of which is
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contained in its own ModuleDecl. For more information, see
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`Clang's documentation for Modules`__.
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7. Shorthand for a "precompiled module file"; effectively "precompiled
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headers" for an entire Clang module. Never used directly by Swift.
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See also `module cache`.
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__ http://clang.llvm.org/docs/Modules.html
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module cache
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Clang's cache directory for precompiled module files. As cache files, these
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are not forward-compatible, and so cannot be loaded by different versions
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of Clang (or programs using Clang, like the Swift compiler). Normally this
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is fine, but occasionally a development compiler will not have proper
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version information and may try to load older module files, resulting in
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crashes in ``clang::ASTReader``.
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open existential
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An `existential` value with its dynamic type pulled out, so that the
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compiler can do something with it.
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PR
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1. "Problem Report": An issue reported in `LLVM's bug tracker`__.
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See also `SR`.
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2. "pull request"
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__ https://llvm.org/bugs/
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primary file
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The file currently being compiled, as opposed to the other files that are
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only needed for context. See also
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`Whole-Module Optimization <WMO (whole-module optimization)>`.
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Radar
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`Apple's bug-tracking system`__, or an issue reported on that system.
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__ https://bugreport.apple.com
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raw SIL
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SIL just after being generated, not yet in a form that can be used for
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IR generation.
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See `mandatory passes <mandatory passes / mandatory optimizations>`.
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resilient
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Describes a type or function where making certain changes will not break
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binary compatibility. See :doc:`LibraryEvolution.rst <LibraryEvolution>`.
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script mode
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The parsing mode that allows top-level imperative code in a source file.
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SIL
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"Swift Intermediate Language". A high-level IR used by the Swift compiler
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for flow-sensitive diagnostics, optimization, and LLVM IR generation.
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-sil-serialize-all
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A mode where all functions in a library are made available for inlining by
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any client, regardless of access control. Also called "magic performance
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mode" as a reminder of how this drastically changes compilation. Not
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guaranteed to work on arbitrary code.
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SR
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An issue reported on `bugs.swift.org <https://bugs.swift.org>`_. A
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backronym for "Swift Report"; really the name is derived from LLVM's
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idiomatic use of "PR" ("Problem Report") for its bugs. We didn't go with
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"PR" for Swift because we wanted to be able to unambiguously reference
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LLVM bugs.
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trap
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A deterministic runtime failure. Can be used as both as a noun ("Using an
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out-of-bounds index on an Array results in a trap") and a verb
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("Force-unwrapping a nil Optional will trap").
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type metadata
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The runtime representation of a type, and everything you can do with it.
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Like a ``Class`` in Objective-C, but for any type.
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value witness table
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A runtime structure that describes how to do basic operations on an unknown
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value, like "assign", "copy", and "destroy". (For example, does copying
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this value require any retains?)
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Only conceptually related to a `witness table`.
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vtable (virtual dispatch table)
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A map attached to a class of which implementation to use for each
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overridable method in the class. Unlike an Objective-C method table,
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vtable keys are just offsets, making lookup much simpler at the cost of
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dynamism and duplicated information about *non*-overridden methods.
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witness
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The value or type that satisfies a protocol requirement.
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witness table
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The SIL (and runtime) representation of a `conformance`; essentially a
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`vtable <vtable (virtual dispatch table)>` but for a protocol instead of
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a class.
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Only conceptually related to a `value witness table`.
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WMO (whole-module optimization)
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A compilation mode where all files in a module are compiled in a single
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process. In this mode there is no `primary file`; all files are parsed,
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type-checked, and optimized together at the SIL level. LLVM optimization
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and object file generation may happen all together or in separate threads. |