[swift-evolution] [SHORT Review] SE-0134: Rename two UTF8-related properties on String

[Ben Rimmington]

<https://github.com/apple/swift-evolution/blob/master/proposals/0134-rename-string-properties.md>

My suggestion for SE-0134 is to use the `utf8CString` name, overloading for CSignedChar and CUnsignedChar:

	<https://github.com/apple/swift/blob/master/stdlib/public/core/CString.swift>

	extension String {
	- init(cString: UnsafePointer<CChar>)
	- init(cString: UnsafePointer<UInt8>)
	- init?(validatingUTF8 cString: UnsafePointer<CChar>)

	+ init(utf8CString: UnsafePointer<CSignedChar>)
	+ init(utf8CString: UnsafePointer<CUnsignedChar>)
	+ init?(validatingUTF8CString: UnsafePointer<CSignedChar>)
	+ init?(validatingUTF8CString: UnsafePointer<CUnsignedChar>)
	}

The properties would change to methods, overloaded by return type:

	<https://github.com/apple/swift/blob/master/stdlib/public/core/StringUTF8.swift>

	extension String {
	- var nulTerminatedUTF8CString: ContiguousArray<CChar>
	- var nulTerminatedUTF8: ContiguousArray<UTF8.CodeUnit>

	+ func utf8CString() -> ContiguousArray<CSignedChar>
	+ func utf8CString() -> ContiguousArray<CUnsignedChar>
	}

## NOTES ##

UTF8.CodeUnit is defined as UInt8, and CChar is currently defined as Int8:

	<https://github.com/apple/swift/blob/master/stdlib/public/core/CTypes.swift>

	/// The C 'char' type.
	///
	/// This will be the same as either `CSignedChar` (in the common
	/// case) or `CUnsignedChar`, depending on the platform.
	public typealias CChar = Int8

	/// The C 'signed char' type.
	public typealias CSignedChar = Int8

	/// The C 'unsigned char' type.
	public typealias CUnsignedChar = UInt8

There's an abandoned proposal to update CChar:

	<http://thread.gmane.org/gmane.comp.lang.swift.evolution/7925/focus=8158>

	<http://thread.gmane.org/gmane.comp.lang.swift.evolution/8419>

String.init(cString: UnsafePointer<UInt8>) and nulTerminatedUTF8CString were added by SE-0107:

	<https://github.com/apple/swift-evolution/blob/master/proposals/0107-unsaferawpointer.md#cstring-conversion>

	<https://github.com/apple/swift/commit/c7aa8284c905a73959ad69255cb56c38db80d039>

Foundation.NSString uses the `utf8String` name instead:

	<https://developer.apple.com/reference/foundation/nsstring/1412128-init>

	<https://developer.apple.com/reference/foundation/nsstring/1411189-utf8string>

-- Ben