SE-0253: Static callables

[Tino]

@Jon_Hull

By making something statically callable, we are saying "treat it like a function". That is, you can call it directly with the normal call syntax for functions

myCallable() //It can be called just like a top level function

I think we agree on that much, the main disagreement is over how to explicitly refer to the function without calling it. I think, because we are treating the callable as a function itself that:

myCallable as func
//or
myCallable as ()->()

...is very natural and does what it says on the tin. referring to myCallable is ambiguous because it can be seen either as an instance of it's type or as a function, so I am telling the compiler which way I want it to be viewed in this instance. Even if we adopt the call syntax, I still think as ()->() should work to refer to the function.

This whole proposal is about objects that can act as something else, isn‘t it?
That is a concept which is quite general, and I wonder wether we may want a general solution:
There has been a proposal for objects to act as an Optional (Introducing `Unwrappable`, a biased unwrapping protocol), and I guess many people would be happy about a way to do calculations with implicit conversions (Float acting as Double...).

Afaik, there are no plans to add such forwarding to Swift, but I‘m also not aware of a decision that those capabilities are unsolicited, so imho it‘s an alternative worth to be considered.