Variadic generics function error

[williamhCode]

I'm writing some code to be converted to wgsl. I tried writing a function called col3 that acts as a vec3 but returns the color converted to linear space. It doesn't seem like the variadic generics is working for vec3 overloads. I tried to implement the function in the playground and it returns this error

USER error: core.meta.slang(2490): error 38203: vector with disallowed element type 'Tuple' encountered
core.meta.slang(2490): error 55200: 'vector<Tuple,3>' is not a supported builtin type for the target.

If I remove where T == float, i get this error

USER error: /user.slang(8): error 30019: expected an expression of type 'float', got 'T'
  return toLin(vec3(expand each args));
                    ^~~~~~
/user.slang(8): error 33070: expected a function, got 'typeof(vec3)'
  return toLin(vec3(expand each args));

Is it out of scope for variadic generics to be able to be passed into function overloads, or a bug?

Code:

import playground;

typealias vec2 = float2;
typealias vec3 = float3;
typealias vec4 = float4;

vec3 col3<each T>(expand each T args) where T == float {
  return toLin(vec3(expand each args));
}

vec3 toLin(vec3 color) {
  return pow(color, vec3(2.2));
}

float4 imageMain(uint2 dispatchThreadID, int2 screenSize)
{
    vec3 color = col3(1.0, 1.0, 1.0);
	return vec4(color, 1.0);
}

[Devon7925]

Looks like slang doesn't handle varargs well in this type of situation. You should create an issue. In general, I think function overrides are better for this situation since using varargs implies the function should be able to take 4+ arguments, when it can't.

[csyonghe]

This is one the key differences between generics and templates.

In a generic type system, the compiler must be able to prove type match before specializing the generics. In this specific case, there is no way for the compiler to know how many elements your args will expand to, and therefore will not be able to match that call to any float3() constructors.

Therefore this error is correct compiler behavior, not a bug.

[williamhCode]

I see, so i guess vargs can only be directly passed to other functions accepting vargs. I'm used to the way c++ does templates so this was a bit surprising.