Code shared from run.dlang.io.

main.d

import std;

struct Vector(uint n, T) if (n > 0 && n <= 3)
{
    T x;
    this(T x)
    {
        this.x = x;
    }

    static if (n >= 2)
    {
        T y;
        this(T x, T y)
        {
            this.x = x;
            this.y = y;
        }
    }
    
    static if (n >= 3)
    {
        T z;
        this(T x, T y, T z)
        {
            this.x = x;
            this.y = y;
            this.z = z;
        }
    }
    
    static if (n >= 4)
    {
        T a;
        this(T x, T y, T z, T a)
        {
            this.x = x;
            this.y = y;
            this.z = z;
            this.a = a;
        }
    }
}

void foo(uint N, T)(Vector!(N, T) vec)
{
    writeln(vec);
}

void main()
{
    Vector!(2, int) vec2;
    Vector!(3, int) vec3;
    foo(vec2);
    foo(vec3);
}