Hi everyone,
We talked about this before when we were discussing mixins, and there seemed to
be generally positive feelings towards it as a feature for the future. I am
fairly certain this affects the ABI though, so I thought I would bring it up
now.
If two protocols have methods/properties with the same name, but different
signatures, we need a way to distinguish between them when attempting to
conform to both.
protocol A {
var x:Int {get set}
}
protocol B {
var x:Double {get set}
}
One possibility is to allow a struct/class/enum to conform to the protocol
while renaming one (or both) of the clashing methods:
struct C: A,B {
var x:Int
var y:Double implements B.x
}
The conforming method/property would still have to have the same signature, but
could have a different name (and parameter labels). It would also allow
protocol methods which have identical signatures and semantics, but different
names to be implemented using the same method (i.e ‘implements D.z & E.w’).
When something is cast to the protocol (say ‘as B’), then calling the property
(e.g. ‘x’) would end up calling the implementation of the renamed property (
‘y’ in this example) on the conforming type.
I think we would also want a way to retroactively conform using existing
properties/methods in an extension declaring conformance. Not sure what the
best syntax for that would be. Off the top of my head (though I would love to
have something with less cruft):
extension D:B {
@conform(to: B.x, with: D.y)
}
or maybe just:
extension D:B {
D.y implements B.x
}
All of this is merely to start the discussion, so feel free to propose better
syntax or a more elegant solution...
Thoughts?
Thanks,
Jon
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