Previously the "as" keyword could either represent coercion or or forced
downcasting. This change separates the two notions. "as" now only means
type conversion, while the new "as!" operator is used to perform forced
downcasting. If a program uses "as" where "as!" is called for, we emit a
diagnostic and fixit.
Internally, this change removes the UnresolvedCheckedCastExpr class, in
favor of directly instantiating CoerceExpr when parsing the "as"
operator, and ForcedCheckedCastExpr when parsing the "as!" operator.
Swift SVN r24253
Metatypes have no user-visible structure, but can at least summarize as their type names. This gives us reasonable ad-hoc Printable behavior (thought debugPrint is still wrong, since a type name isn't parsable without being .self'ed).
Swift SVN r23745
Per API review with Ali. While we're here, give the initializer a corresponding 'rawValue' argument label, and change the associated type name to RawValue to match.
Swift SVN r21888
Redefine the RawRepresentable protocol to use an 'init?' method instead of 'fromRaw(Raw)', and a 'raw' get-only property instead of 'toRaw()'. Update the compiler to support deriving conformances for enums and option sets with the new protocol. rdar://problem/18216832
Swift SVN r21762
