[swift-evolution] [Draft] Change @noreturn to unconstructible return type

Thorsten Seitz tseitz42 at icloud.com
Wed Jun 8 00:41:08 CDT 2016

Am 08.06.2016 um 01:36 schrieb Brent Royal-Gordon via swift-evolution <swift-evolution at swift.org>:

>> A return type makes a lot of sense linguistically but does not cover all practical cases because you might not be the one deciding what the function's signature is. For example, you might implement a protocol method that is non-optional, but you never expect to be called. The only way to indicate that to the compiler is with an attribute.
> If Swift permits return type covariance—that is, for an override or implementation to tighten the return type—then this will happen naturally: Never is a subtype of all types, so you can validly change any return type to Never and meet the supertype's requirements.

Good point!

> I believe Swift supports return type covariance for overridden methods, but not for protocol requirements. This is, in my opinion, an incorrect behavior which should be changed.



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> Brent Royal-Gordon
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