[swift-evolution] [Pitch] Non-class type requirements on protocols (eg : struct, : enum)

[Xiaodi Wu]

What's your use case for distinguishing structs and enums?
On Fri, Oct 21, 2016 at 1:40 AM Mike Kasianowicz via swift-evolution <
swift-evolution at swift.org> wrote:

> Currently protocols can have the class constraint:
> protocol MyProtocol : class {}
>
> It would be (a) intuitive and (b) useful to allow such things as:
> protocol Model : struct {} or protocol Event : enum {}
>
> These types of restrictions can help prevent accidental anti-patterns or
> misuse of APIs.
>
> Seems simple and non-controversial... right?
>
> [Note: I'd like to see even more heavy-handed protocol restrictions in the
> future.  For example, a protocol describing an enum with a common case, or
> a struct with no reference members. Great stuff for defensively coding
> APIs.]
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