proposed @noreturn attribute

[Walter Bright via Digitalmars-d]

On 7/8/2017 9:23 PM, Meta wrote:
> On Sunday, 9 July 2017 at 02:25:50 UTC, Walter Bright wrote:
>> (D already has a `void` type, so can't use Haskell's word.)
> 
> Just so we are all on the same page, from a type-theory perspective void is a 
> unit type (it has 1 value), not an uninhabited type (it has no values, i.e. 
> Haskell's _|_ (bottom) type).
> 
> A function with a return type of unit means "this function returns no useful 
> information", because the type only has one possible value anyway. A function 
> with a return type of bottom means "this function can never return", because 
> there is no value of type bottom that could be returned. All that can be done is 
> for the function to diverge (throwing an exception, ending the program, looping 
> forever, etc.).

Thanks for the explanation.


> We sort of have this already with `assert(0)`. The compiler knows that no 
> execution can take place after an `assert(0)` is encountered (in other words, it 
> knows that the function diverges). We just don't have a corresponding type to 
> represent this (Rust uses ! but if I remember correctly it's not quite a first 
> class type).
> 
> If we wanted to be cute we could use `typeof()` to represent this type as there 
> is no value you can give to typeof such that it returns the bottom type. It also 
> avoids having to come up with some special symbol or name for it.

That is indeed an interesting idea. Thanks!

(This thread is turning out to be more productive than I anticipated.)