[swift-evolution] Multiple protocols variable - automatic class-type inference

Jordan Rose jordan_rose at apple.com
Tue Jul 5 12:54:38 CDT 2016

The case with testVar4 and testVar5 is not exactly a bug—the default implementation of a mutating protocol requirement can reassign 'self' even if the dynamic type turns out to be a class. (I'm not sure that's a good feature, but it is the current behavior of Swift 3.) I agree that we should resolve the contradiction at the end somehow, though.


> On Jul 5, 2016, at 8:39, Charlie Monroe via swift-evolution <swift-evolution at swift.org> wrote:
> These feel like bugs in the compiler. I'd suggest filing a bug report at http://bugs.swift.org <http://bugs.swift.org/> if others don't think there is more to it...
>> On Jul 4, 2016, at 12:47 AM, Jakub Skotnicki via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Hi,
>> I would like to make a proposal for automatic class-type inference for a variable which conforms to multiple protocols. I have not seen any similar proposals on swift-evolution <https://github.com/apple/swift-evolution> site, also these in the rejected section, that is why I am mailing it to discuss. 
>> What is it about? (picture below - code with explanations):
>> <swift.png>
>> Conclusion:
>> Multiple protocols constant variable should have its properties mutable if at least one of the protocols is a class-protocol. Firstly, this solves a problem of changing this variable to mutable (with var keyword), which can simply be undesirable, and currently leads to a paradox warning if done on a method parameter. Secondly, it solves a problem of changing specified protocols to class-protocols in order to modify any properties or use mutating function on such variables, which could be an unwanted constrain or it is simply impossible in cases where specified protocols iare also implemented by non-class types.
>> I believe it has no impact on existing code. It will simply start to work.
>> Please let me know what you think about it.
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