Open Radar

 
Summary:
I have a function composition operator defined like so in Prelude.framework[1]:

public func >>> <T, U, V> (f: T -> U, g: U -> V) -> T -> V {
	return { g(f($0)) }
}

Now I want to use it to implement Either.map[2]:

extension Either {
	public func map<V>(f: U -> V) -> Either<T, V> {
		return either(ifLeft: Either<T, V>.left, ifRight: f >>> Either<T, V>.right)
	}
}

Great! Being a good citizen I now want to mark map’s parameter as @noescape. However, if I do that, I can’t use >>> to compose f with the Either.right static function, because I don’t have a way to indicate to Swift that the operands to >>> will not escape if the returned closure does not escape. As a result, I have to either forego @noescape, or forego my composition operator.

I’d love to be able to tell Swift that >>>’s operands are captured completely by its returned closure and do not otherwise escape it.


Steps to Reproduce:
N/A

Expected Results:
N/A

Actual Results:
N/A

Regression:
N/A

Notes:
1: https://github.com/robrix/Prelude
2: https://github.com/robrix/Either