[swift-evolution] [Draft] Allow multiple conformances to the same protocol

[Jordan Rose]

Associated types aren't generic parameters; the whole point is that they're requirements, just like the other declarations in a protocol.

You might be trying to invent generic protocols instead, which (IIRC) aren't inherently a bad thing. But I think this needs a lot more fleshing out before it can really be discussed—it's hard to know how you can and can't use these things, and how they might be implemented.

Best,
Jordan


> On Jun 8, 2016, at 12:07, Антон Жилин via swift-evolution <swift-evolution at swift.org> wrote:
> 
> ==Motivation==
> 
> protocol From {
>     associatedtype FromType
>     init(_ value: FromType)
> }
> 
> The problem is, one type cannot implement multiple From "conversions".
> 
> ==Proposed solution==
> 
> Allow specifying all associated types using generic syntax.
> 
> extension Int : From<Float> { }
> extension Int : From<Double> { }
> 
> This is only allowed in conformance declarations.
> 
> ==Future directions==
> 
> We can replace all *Convertible protocols with From and Into, which will be defined similarly to Rust.
> 
> - Anton
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