struct Foo
{
    ubyte x, y, z;
}

auto hash(T)(T[] values...)
{
    int[T] result;
    
    foreach (value; values)
    {
        result[value] = 0;
    }
    
    return result;
}

void main()
{
    auto red   = Foo(255, 0, 0);
    auto green = Foo(0, 255, 0);
    auto blue  = Foo(0, 0, 255);
    
    auto color = Foo(0, 0, 255);
    
    assert(color in hash(red, green, blue));
}