[swift-evolution] [Discussion] Modernizing Attribute Case and Attribute Argument Naming

[Brent Royal-Gordon]

> @Autoclosure // was @autoclosure
> @Available // was @available
> @ObjC // was @objc
> @NoEscape // was @noescape
> @NonObjC // was @nonobjc
> @NoReturn // was @noreturn
> @Testable // was @testable
> @WarnUnusedResult // was @warn-unused-result
> @Convention  // was @convention
> @NoReturn // was @noreturn
> 
> In the revised design, the following example for Swift 2.2
> 
> @warn_unused_result(mutable_variant="sortInPlace")
> public func sort() -> [Self.Generator.Element]
> 
> becomes
> 
> @WarnUnusedResult(mutableVariant: "sortInPlace")
> public func sort() -> [Self.Generator.Element]

Wow, I'm surprised by how much I hate this. Currently, all Swift keywords are entirely lowercase (ignoring things like `Type`, `Protocol`, and `dynamicType` which come after a dot). I think I've learned to half-ignore things that look like that, but capitalizing suddenly pulls the spotlight onto these keywords. I'm just not a fan.

I think we're better off renaming or redesigning `warn_unused_result` so that it's readable when it's all-lowercase with no underscores. Some ideas:

	@onlyreturns func sorted() -> [Self.Generator.Element]
	func sorted() -> @important [Self.Generator.Element]

Alternatively, we could reverse the semantic and make all all non-Void functions warn unless they have an attribute saying not to.

	@ignoreresult mutating func updateValue(value: Value, forKey key: Key) -> Value?
	mutating func updateValue(value: Value, forKey key: Key) -> @ignorable Value?
	mutating func updateValue(value: Value, forKey key: Key) -> @convenience Value?

If we do that, we'll likely still want to be able to annotate non-mutating methods with their mutating variants (well, unless we think the compiler can guess based on the API Guidelines.)

	@variant(mutating: "sort") func sorted() -> [Self.Generator.Element]
	@alternative(mutating: "sort") func sorted() -> [Self.Generator.Element]

That opens the possibility of using `@variant(nonmutating:)` on mutating functions, too.

-- 
Brent Royal-Gordon
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