Need for std.meta.isSame over __traits(isSame)

[user1234]

On Wednesday, 1 September 2021 at 22:51:40 UTC, Per Nordlöw wrote:
> Can somebody explain the need for
>
> ```d
> private template isSame(alias a, alias b)
> {
>     static if (!is(typeof(&a && &b)) // at least one is an 
> rvalue
>             && __traits(compiles, { enum isSame = a == b; })) 
> // c-t comparable
>     {
>         enum isSame = a == b;
>     }
>     else
>     {
>         enum isSame = __traits(isSame, a, b);
>     }
> }
> ```
>
> when there is already
>
> ```d
> __traits(isSame, a, b)
> ```
>
> ?
>
> Are there any cases where
>
> ```d
> __traits(isSame, a, b)
> ```
>
> doesn't have the same value as
>
> ```d
> a == b
> ```
>
> provided the static if expression above is true.

the traits does not work on literals passed by 
_AliasTemplateParameter_.

```d
enum isSame1(alias a, alias b) = a == b;
enum isSame2(alias a, alias b) = __traits(isSame, a, b);

pragma(msg, isSame1!(0, 0));   // true
pragma(msg, isSame2!(0, 0));   // false
```

This looks a bit like a bug, because `__traits(isSame, 0, 0)` 
yields `true`