• WebFreak001 (13/13) Apr 21 2022 What would you expect for this code?
• rikki cattermole (4/4) Apr 21 2022 noreturn is the bottom type which can implicitly convert to any type,
• WebFreak001 (10/14) Apr 21 2022 ok so I guess all the `isSomething(T)` functions must be written
• rikki cattermole (3/3) Apr 21 2022 Could we add a check for this in DScanner?
• Dennis (11/13) Apr 21 2022 What issue do you have with it returning `true`? Note that this
• Paul Backus (5/9) Apr 21 2022 Presumably the problem is that if you write something like

WebFreak001 <d.forum webfreak.org> writes:

What would you expect for this code?

```d
struct Something(Types...) {}

enum isSomethingExact(T) = is(T == Something!Types, Types...);
enum isSomething(T) = is(T : Something!Types, Types...);

pragma(msg, isSomethingExact!noreturn);
pragma(msg, isSomething!noreturn);
```

This currently outputs `false`, `true` which breaks my code 
because more concretely `isSumType!(typeof(someMethod()))` 
returns true. I can add a check for noreturn before that, but it 
seems a little weird that noreturn returns true for isSomething!T 
and functions like that in phobos.

rikki cattermole <rikki cattermole.co.nz> writes:

noreturn is the bottom type which can implicitly convert to any type, 
including void. A value of type noreturn will never be produced and the 
compiler can optimize such code accordingly.

https://dlang.org/spec/type.html#noreturn

WebFreak001 <d.forum webfreak.org> writes:

On Thursday, 21 April 2022 at 12:28:37 UTC, rikki cattermole 
wrote:
 noreturn is the bottom type which can implicitly convert to any 
 type, including void. A value of type noreturn will never be 
 produced and the compiler can optimize such code accordingly.

 https://dlang.org/spec/type.html#noreturn

ok so I guess all the `isSomething(T)` functions must be written 
like this then:

```d
enum isSomething(T) = !is(immutable T == immutable noreturn)
     && is(T : Something!Other, Other...);
```

which I think is a little bug-prone, but at least that would 
solve my issues.

rikki cattermole <rikki cattermole.co.nz> writes:

Could we add a check for this in DScanner?

Otherwise I'm not sure how else we are going to find all of these 
instances and fix them.

Dennis <dkorpel gmail.com> writes:

On Thursday, 21 April 2022 at 12:41:08 UTC, WebFreak001 wrote:
 which I think is a little bug-prone, but at least that would 
 solve my issues.

What issue do you have with it returning `true`? Note that this 
compiles:
```D
 safe:
import std.sumtype;
void main()
{
     SumType!(int, string) s = assert(0);
}

```

Paul Backus <snarwin gmail.com> writes:

On Thursday, 21 April 2022 at 12:54:12 UTC, Dennis wrote:
 On Thursday, 21 April 2022 at 12:41:08 UTC, WebFreak001 wrote:
 which I think is a little bug-prone, but at least that would 
 solve my issues.

 What issue do you have with it returning `true`?

Presumably the problem is that if you write something like 
`assert(0).match!();`, you get a spew of compiler errors, on 
account of the fact that `match` assumes anything that satisfies 
`isSumType` has properties like `Types` and `get!T`.