swift234

Use UTF-16 string literals when the (builtin) string literal type supports it.

Make the compiler fully support both UTF-8 and UTF-16 string
literals. A (standard-library-defined) string type (such as String)
that wants UTF-16 string literals should conform to the
BuiltinUTF16StringLiteralConvertible protocol; one that wants UTF-8
string literals should conform to the BuiltinStringLiteralConvertible
protocol.

Note that BuiltinUTF16StringLiteralConvertible inherits from
BuiltinStringLiteralConvertible, so a string type that wants UTF-16
string literals also has to implement support for UTF-8. The UTF-16
entry point is preferred when the compiler knows that UTF-16 is
supported. This only tends to happen when we have a generic parameter
that is required to conform to StringLiteralConvertible, e.g.,

  func f<T: StringLiteralConvertible>() {
    var t: T = "Hello, World!" // uses UTF-8 entry point
  }

because the UTF-8 entry point is the only one guaranteed to be available.



Swift SVN r12014