[swift-evolution] Idea: change "@noreturn func f()" to "func f() noreturn"

Jordan Rose jordan_rose at apple.com
Thu Feb 25 17:04:13 CST 2016

"noreturn" is a part of a type signature; a @noreturn method cannot be overridden by a method that isn't @noreturn*, and you could have a closure that's guaranteed to not return.

* This isn't true in Objective-C, but it is in Swift.


> On Feb 25, 2016, at 14:38, Radosław Pietruszewski via swift-evolution <swift-evolution at swift.org> wrote:
> The difference though is that throws/rethrows is a part of type signature, @noreturn isn’t and has no reason to be AFAICT. It’s just an attribute of the method…
> — Radek
>> On 25 Feb 2016, at 22:44, Jacob Bandes-Storch via swift-evolution <swift-evolution at swift.org <mailto:swift-evolution at swift.org>> wrote:
>> Premise: there are multiple ways of describing control-/data-flow when a function is called:
>>     func x() -> T   // x returns a value, of type T, to the caller
>>     func x() throws  // x may throw an error to the caller
>>     func x() throws -> T  // x may throw an error, and also return a value
>>     func x(...) rethrows ... // if a closure argument can throw an error, x may also throw
>>     @noreturn func x()  // x never returns to the caller
>> "noreturn" is currently spelled as an attribute, but like "throws" / "rethrows" / "-> T", it's really describing how control flow works.
>> IMO this calls for consistency: whatever happens "after" the function is called should appear "after" the parameter list.
>>     func x() noreturn {
>>         ...
>>     }
>> Thoughts?
>> Jacob
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