template alias that includes a parameter

[Timoses]

On Sunday, 1 July 2018 at 01:48:15 UTC, Simen Kjærås wrote:
>
> I'd send you straight to std.meta.ApplyLeft, but it seems to do 
> the wrong thing here, in that it doesn't handle IFTI. This 
> thing does:
>
> void fooImpl(int n, T)(const T line) { }
>
> unittest {
>     alias fun = applyLeft!(fooImpl, 3);
>     fun(`aaa`);
>     applyLeft!(fooImpl, 3)(`aaa`);
> }
>
> template applyLeft(alias Fn, T...) {
>     auto applyLeft(U...)(U args) {
>         return Fn!T(args);
>     }
> }

Would be nice if std.meta.ApplyLeft did the job here.. Is there 
no way of achieving that?
It's current implementation looks like this:

template ApplyLeft(alias Template, args...)
{
     alias ApplyLeft(right...) = SmartAlias!(Template!(args, 
right));
}

private template SmartAlias(T...)
{
     static if (T.length == 1)
     {
         alias SmartAlias = Alias!T;
     }
     else
     {
         alias SmartAlias = AliasSeq!T;
     }
}

Would have to find a way to determine whether Template would 
resolve to a function or not. Can't find anything in Traits[1] or 
std.traits[2]. Template inspection looks rather limited : /.

[1]: https://dlang.org/spec/traits.html
[2]: https://dlang.org/phobos/std_traits.html