[swift-evolution] Mark protocol methods with their protocol

[Vladimir.S]

On 20.09.2016 19:03, Charles Srstka wrote:
>> On Sep 20, 2016, at 10:56 AM, Vladimir.S via swift-evolution
>> <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>>
>> Then, shouldn't we disallow protocol conformance 'in-place' in type's
>> definition? So, if you need to conform to protocol - only extension is
>> the syntax for this. In this case I can understand the idea. Otherwise -
>> can't.
>
> You can’t completely restrict protocol conformance to extensions, because
> extensions can’t contained stored properties. Thus, to satisfy a protocol
> requirement with a stored property, it must be placed in the type’s definition.

Oh, yes, of course.. And as soon as we can have default implementations for 
props also - this solution can't help compiler to notify us if our property 
defined as implementation for protocol requirement is not playing this role 
any more.
Or we we need stored properties in extensions for this idea. As I 
understand, there were some discussions regarding this.

In any case the solution "protocol conformance in extensions" does not help 
when we deal with protocol default implementations - we can't say to 
compiler that this method/prop here exactly as implementation for protocol, 
not helper method. I.e. in this situation:

protocol A {
     func foov()
}

protocol B : A {
}

extension A {
     func foov() {}
}

extension B {
     // I was expecting this is a default implementation of foov() for B
     // but in reality this is a helper method
     // who knows when this error will be detected
     func foow() {}
}

I think protocol programming should not be so fragile as it is now and so 
compiler should help in any place where it can help. For now I don't see 
any better idea than require here some keyword like `override` or `implement`.

>
> Charles
>