Am 21.07.2021 um 09:16 schrieb bauss:
> Is there a way to make this logic work without using a mixin template.
> 
> I'd prefer if using a plain template was possible, rather than using a mixin template, because it introduces some extra boilerplate.

The symbol name is not available in the scope of the template, so that the `mixin(symbol.stringof)` doesn't work, but you can simply use the alias directly:

    template CanCompile(alias symbol)
    {
        enum CanCompile = __traits(compiles, { symbol = 10; });
    }

But why do you think that `CanCompile` fails? It works for me:
```D
template CanCompile(alias symbol)
{
    enum CanCompile = __traits(compiles, { symbol = 10; });
}

mixin template CanCompile2(alias symbol)
{
    enum couldCompile = __traits(compiles, { symbol = 10; });
}

void main()
{
    int x = 20;

    static if (CanCompile!x)
    {
        x = 9;
    }

    assert(x == 9);

    mixin CanCompile2!x;
    static if (couldCompile)
    {
        x = 12;
    }

    assert(x == 12);
}
```

On Wednesday, 21 July 2021 at 09:06:52 UTC, Sönke Ludwig wrote:
> Am 21.07.2021 um 09:16 schrieb bauss:
>> Is there a way to make this logic work without using a mixin template.
>> 
>> I'd prefer if using a plain template was possible, rather than using a mixin template, because it introduces some extra boilerplate.
>
> The symbol name is not available in the scope of the template, so that the `mixin(symbol.stringof)` doesn't work, but you can simply use the alias directly:
>
>     template CanCompile(alias symbol)
>     {
>         enum CanCompile = __traits(compiles, { symbol = 10; });
>     }

The problem is that I just saw I didn't describe my problem very well, as I don't actually have the symbol at the given time.

I only had the symbol name and I use it to test if the symbol is available because it comes from a __traits(allMembers) which includes some symbols that makes it fail to compile if I try to use the symbol directly without checking whether it compiles or not.

And this was the exact template I was trying to use:

```d
template CanUseSymbol(string symbolName, string symbolAlias = "symbol", string moduleAlias = "moduleImport")
{
  enum CanUseSymbol = __traits(compiles, { mixin("alias " ~ symbolAlias ~ " = " ~ moduleAlias ~ "." ~ symbolName ~ ";"); });
}
```

For obvious reasons it doesn't work as you also mentioned, the scope simply isn't available.

But I can't use alias unfortunately in this case.

I wish there was a way to return the symbols from allMembers, instead of just the name of the symbols, that would solve this problem.

On Wednesday, 21 July 2021 at 10:08:10 UTC, bauss wrote:
> On Wednesday, 21 July 2021 at 09:06:52 UTC, Sönke Ludwig wrote:
>> Am 21.07.2021 um 09:16 schrieb bauss:
>>> Is there a way to make this logic work without using a mixin template.
>>> 
>>> I'd prefer if using a plain template was possible, rather than using a mixin template, because it introduces some extra boilerplate.
>>
>> The symbol name is not available in the scope of the template, so that the `mixin(symbol.stringof)` doesn't work, but you can simply use the alias directly:
>>
>>     template CanCompile(alias symbol)
>>     {
>>         enum CanCompile = __traits(compiles, { symbol = 10; });
>>     }
>
> The problem is that I just saw I didn't describe my problem very well, as I don't actually have the symbol at the given time.
>
> I only had the symbol name and I use it to test if the symbol is available because it comes from a __traits(allMembers) which includes some symbols that makes it fail to compile if I try to use the symbol directly without checking whether it compiles or not.
>
> And this was the exact template I was trying to use:
>
> ```d
> template CanUseSymbol(string symbolName, string symbolAlias = "symbol", string moduleAlias = "moduleImport")
> {
>   enum CanUseSymbol = __traits(compiles, { mixin("alias " ~ symbolAlias ~ " = " ~ moduleAlias ~ "." ~ symbolName ~ ";"); });
> }
> ```
>
> For obvious reasons it doesn't work as you also mentioned, the scope simply isn't available.
>
> But I can't use alias unfortunately in this case.
>
> I wish there was a way to return the symbols from allMembers, instead of just the name of the symbols, that would solve this problem.

I found a somewhat solution to it all by creating a template that used __traits(allMembers) and in the same scope tested the members and built a new list of members that were available and then simply used the generated list to loop through, so I didn't have to test the symbols outside of the template's scope.