[swift-evolution] Apply for closure

[Tino Heth]

I have no obvious use case, but I like the concept of "functions having functions":
It is most likely not that relevant for Swift 3, but as soon as the macro-system becomes concrete, it could be valuable for meta-programming…

Besides "apply", we could have introspection ("f.parametersByIndex[0].type") and a revival of currying
let twice: (Double) -> Double = *.curry(parameterIndex: 0, value: 2.0)

It could even be possible to do meta-programming without leaving the language, e.g.

class Snitch: SomeClass {
	for f in super.overridableMethods {
		self.implementation[f] = { (args: f.argumentTuple) in
			print("Function \(f.name) has been called with \(args)")
			return f.apply(args)
		}
	}
}

I probably would hate anyone actually using such a feature (unless the debugger is really great ;-), but it would be freaking cool nonetheless ;-)

Tino