What would you expect for this code?

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.

On Thursday, 21 April 2022 at 12:28:37 UTC, rikki cattermole wrote:

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

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.

On Thursday, 21 April 2022 at 12:41:08 UTC, WebFreak001 wrote:

What issue do you have with it returning true? Note that this compiles:

@safe:
import std.sumtype;
void main()
{
    SumType!(int, string) s = assert(0);
}

On Thursday, 21 April 2022 at 12:54:12 UTC, Dennis wrote:

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.