[swift-evolution] Renaming for Protocol Conformance

[Charles Srstka]

I was just thinking about proposing something like this.

+1.

Charles

> On Aug 22, 2016, at 11:59 PM, Jonathan Hull via swift-evolution <swift-evolution at swift.org> wrote:
> 
> 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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