[swift-users] fileprivate extensions can't add protocol conformance

[Slava Pestov]

> On Feb 13, 2017, at 11:57 PM, Alejandro Martinez via swift-users <swift-users at swift.org> wrote:
> 
> "is currently required to have the same visibility as the protocol itself"
> 
> that makes sense. I guess my question is more, is there a technical
> reason for it?

The runtime and compiler do not support ‘non public’ conformances yet. We’ve started some of the plumbing required for this in the compiler because it is needed for other reasons (see my on-going SubstitutionMap work). However there are some interesting issues to resolve if we want to add this as a feature, in particular, around the behavior of dynamic casts.

Slava

> 
> On Mon, Feb 13, 2017 at 4:35 PM, Paul Schmidt
> <paul.schmidt at smartsheet.com> wrote:
>> Would love for this to be possible. It becomes an issue in mixed code: if
>> you include conformance to a <foo>Kit protocol in one of your Swift classes,
>> then you have to include the corresponding headers in every Objective C file
>> that includes the bridging .h file. The <foo>Kit classes are added to the
>> bridging header, but not the protocols. There are workarounds (such as using
>> an instance of a conforming nested class as a proxy- nested classes are not
>> emitted in the bridging header), but it's so much cleaner to be able conform
>> to the protocol privately. (Either that, or fix the utility that builds the
>> bridging header so it exposes the protocol as well.)
>> 
>> 
>> 
>> 
>> Paul Schmidt | Smartsheet
>> Senior iOS Software Development Engineer
>> E: paul.schmidt at Smartsheet.com
>> C: 425.283.9576
>> 
>> Work Better™
>> Learn More → smartsheet.com
>> 
>> On Mon, Feb 13, 2017 at 8:28 AM, Alejandro Martinez via swift-users
>> <swift-users at swift.org> wrote:
>>> 
>>> Hi,
>>> 
>>> I found myself writting some method that parsed an API response and
>>> wanted to use Decodable to map the response into a struct declared
>>> elsewhere.
>>> My idea was that each api response handler file (I use completely
>>> different APIs that map into the same model) could add it's own
>>> fileprivate conformance to decodable into the model struct so each api
>>> response handler would use a different decoding function. But I found
>>> the compiler telling me that is not possible.
>>> 
>>> I can easily change my design, is not an issue but I'm super curious.
>>> Why fileprivate extensions can't add protocol conformance? Is there a
>>> technical reason behind? or a conscience design?
>>> 
>>> Thanks!
>>> 
>>> 
>>> --
>>> Alejandro Martinez
>>> http://alejandromp.com
>>> _______________________________________________
>>> swift-users mailing list
>>> swift-users at swift.org
>>> https://lists.swift.org/mailman/listinfo/swift-users
>> 
>> 
> 
> 
> 
> -- 
> Alejandro Martinez
> http://alejandromp.com
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