I'm having issues when trying to use a template alias as a template specialisation.
When using the following:
> alias Vec(uint size, Type) = Mat!(size, 1, Type);

> void setUniform(V : Vec!(L, bool), int L)(string name, V value) {...}

> Vec!(4, bool) a;
> setUniform("test", a);

I get the following error:
> template `shader.Shader.setUniform` cannot deduce function from argument types `!()(string, Mat!(4u, 1u, bool))`, candidates are:DUB
shader.d(43, 7): `setUniform(V : Vec!(L, bool), uint L)(string name, V value)`

Meanwhile, when using the following, I have no issues:
> void setUniform(V : Mat!(L, 1, bool), int L)(string name, V value) {}

On Saturday, 16 January 2021 at 01:21:24 UTC, Paul wrote:
> I'm having issues when trying to use a template alias as a template specialisation.
> When using the following:
>> alias Vec(uint size, Type) = Mat!(size, 1, Type);
>
>> void setUniform(V : Vec!(L, bool), int L)(string name, V value) {...}
>
>> Vec!(4, bool) a;
>> setUniform("test", a);
>
> I get the following error:
>> template `shader.Shader.setUniform` cannot deduce function from argument types `!()(string, Mat!(4u, 1u, bool))`, candidates are:DUB
> shader.d(43, 7): `setUniform(V : Vec!(L, bool), uint L)(string name, V value)`
>
> Meanwhile, when using the following, I have no issues:
>> void setUniform(V : Mat!(L, 1, bool), int L)(string name, V value) {}

You have encountered issue 1807:

https://issues.dlang.org/show_bug.cgi?id=1807

The easiest way to work around it that I know of is to change `Vec` from an alias into a struct:

struct Vec(uint size_, Type)
{
    Mat!(size, 1, Type) payload;
    alias payload this;
}

On Saturday, 16 January 2021 at 01:38:38 UTC, Paul Backus wrote:
> You have encountered issue 1807:
>
> https://issues.dlang.org/show_bug.cgi?id=1807

Ah I see, thank you, sad to see several DIP's I'd be interested in are postponed :(
Thanks for the workaround hint, I'll probably be using that.

On Saturday, 16 January 2021 at 01:21:24 UTC, Paul wrote:
> I'm having issues when trying to use a template alias as a template specialisation.
> When using the following:
>> alias Vec(uint size, Type) = Mat!(size, 1, Type);
>
>> void setUniform(V : Vec!(L, bool), int L)(string name, V value) {...}
>
>> Vec!(4, bool) a;
>> setUniform("test", a);
>
> I get the following error:
>> template `shader.Shader.setUniform` cannot deduce function from argument types `!()(string, Mat!(4u, 1u, bool))`, candidates are:DUB
> shader.d(43, 7): `setUniform(V : Vec!(L, bool), uint L)(string name, V value)`
>
> Meanwhile, when using the following, I have no issues:
>> void setUniform(V : Mat!(L, 1, bool), int L)(string name, V value) {}

In this case you can use a const template parameter:

  alias Vec(uint size, Type, const uint length = 1) = Mat!(size, length, Type);

Although this is not a generic workaround for the issue mentioned.