enum BoolEnum   : bool   { TestBool   = false }
enum CharEnum   : char   { TestChar   = 'A' }
enum StringEnum : string { TestString = "Hello" }

pragma(msg, isBoolean!BoolEnum);       // true
pragma(msg, isSomeChar!CharEnum);      // true
pragma(msg, isSomeString!StringEnum);  // false

Why does isSomeString not return true for an enum with base type string while
other isX functions return true for enums with an according base type X?
Regarding whether enums should be considered by these functions, I can see the
case being made one of both ways (personally, I'd say they should), but in the
example above it seems that different rules are applied.

On Sunday, 14 March 2021 at 10:42:17 UTC, wolframw wrote:
> enum BoolEnum   : bool   { TestBool   = false }
> enum CharEnum   : char   { TestChar   = 'A' }
> enum StringEnum : string { TestString = "Hello" }
>
> pragma(msg, isBoolean!BoolEnum);       // true
> pragma(msg, isSomeChar!CharEnum);      // true
> pragma(msg, isSomeString!StringEnum);  // false
>
> Why does isSomeString not return true for an enum with base type string while
> other isX functions return true for enums with an according base type X?
> Regarding whether enums should be considered by these functions, I can see the
> case being made one of both ways (personally, I'd say they should), but in the
> example above it seems that different rules are applied.

May be a regression?

https://issues.dlang.org/show_bug.cgi?id=16573

On Sunday, 14 March 2021 at 16:09:39 UTC, Imperatorn wrote:
> On Sunday, 14 March 2021 at 10:42:17 UTC, wolframw wrote:
>> enum BoolEnum   : bool   { TestBool   = false }
>> enum CharEnum   : char   { TestChar   = 'A' }
>> enum StringEnum : string { TestString = "Hello" }
>>
>> pragma(msg, isBoolean!BoolEnum);       // true
>> pragma(msg, isSomeChar!CharEnum);      // true
>> pragma(msg, isSomeString!StringEnum);  // false
>>
>> Why does isSomeString not return true for an enum with base type string
>
> May be a regression?
>
> https://issues.dlang.org/show_bug.cgi?id=16573

Indeed: https://run.dlang.io/is/liSDBZ

It regressed in 2.079.1. Seems to be worth an issue report.

—Bastiaan.

On Sunday, 14 March 2021 at 16:30:47 UTC, Bastiaan Veelo wrote:
> On Sunday, 14 March 2021 at 16:09:39 UTC, Imperatorn wrote:
>> On Sunday, 14 March 2021 at 10:42:17 UTC, wolframw wrote:
>>> [...]
>>
>> May be a regression?
>>
>> https://issues.dlang.org/show_bug.cgi?id=16573
>
> Indeed: https://run.dlang.io/is/liSDBZ
>
> It regressed in 2.079.1. Seems to be worth an issue report.
>
> —Bastiaan.

Thanks for the advice. I've since had a deeper look into this located the PR
that changed this behavior [1]. It seems this change was very much deliberate.
In the PR, Jonathan also makes some points that are very hard to disagree with.
So, perhaps the better solution would be to make isBoolean and isSomeChar (and
perhaps other functions that I didn't think of) return false for enums?

As a side note, isSomeChar returning true for enums is also what causes the
behavior demonstrated in Issue 21639 [2].

[1] https://github.com/dlang/phobos/pull/5291
[2] https://issues.dlang.org/show_bug.cgi?id=21639