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

[Radosław Pietruszewski]

Ah, that’s a neat idea! Not sure it’s an improvement though to have a magic type that changes how the compiler treats your method, rather than a rather explicit *attribute* on the method…

— Radek

> On 25 Feb 2016, at 23:12, Joe Groff via swift-evolution <swift-evolution at swift.org> wrote:
> 
>> 
>> On Feb 25, 2016, at 1:44 PM, 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?
> 
> We really don't even need a special syntactic form or attribute for 'no return' at all. We could provide a standard unconstructible type:
> 
> public /*closed*/ enum NoReturn {}
> 
> and it would be impossible for a function that returns NoReturn to return normally.
> 
> -Joe
> 
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