[DRAFT] Introduce @specialize attribute

[airspeedswift]

No description provided.

[eeckstein]

@al45tair recently brought up this feature request, which might be good to add in "future directions":

@_specialize only appears to affect functions/methods. That makes sense from an implementation perspective, but it would be nice to be able to write @_specialize on a class or struct to get Swift to specialise all the methods that are affected by the generics on that class or struct without having to write @_specialize before every single one.

[airspeedswift]

it would be nice to be able to write @_specialize on a class or struct

Hmm. There are lots of open questions here. For example, would that get applied to methods added outside the module? I guess it could. That's quite a subtle at-a-distance impact though.

[al45tair]

Hmm. There are lots of open questions here. For example, would that get applied to methods added outside the module? I guess it could. That's quite a subtle at-a-distance impact though.

That's a great question. I'm not sure whether that's desirable; maybe it should only apply within the defining module, and if someone wants to extend the class and have things specialised they should have to write @_specialize on their extension?