Questions about opAssign alternate and template quality

[nobody]

Oskar Linde wrote:

>> My second question is mostly an open invitation to make suggestions 
>> for improving my template writing style. In particular I am suspicious 
>> that there is a way to take better advantage of templates and not 
>> write out all 60 permutations.
>>
>> So here is the actual code. I only included the RGB permutations to 
>> keep it as short as possible.
> 
> Implicit function template instantiation and some static ifs can help 
> you. Unfortunately, IFTI isn't yet implemented for member functions, but 
> you can make a free function like:
> void pixAssign(A,B)(out A A, in B b) {
>         static if (is(a.a) && is(b.a)) {
>                 // Alpha
>                 a.a = b.a;
>         } else static if(is(a.a)) {
>                 a.a = typeof(a.a).max;
>         }
>         static if (is(a.r) && is(b.r)) {
>                 // RGB->RGB
>                 auto r = b.r;
>                 auto g = b.g;
>                 auto b = b.b;
>                 a.r = r;
>                 a.g = g;
>                 a.b = b;
>         } else static if (is(a.h) && is(b.h)) {
>                 // HLS -> HLS
>                 auto h = b.h;
>                 auto l = b.l;
>                 auto s = b.s;
>                 a.h = h;
>                 a.l = l;
>                 a.s = s;
>         } else static if(is(a.r)) {
>                 // HLS -> RGB
>                 assert(0,"not implemented.");
>         } else static if(is(b.r)) {
>                 // RGB -> HLS
>                 assert(0,"not implemented.");
>         }
> }
> 
> Which should take care of all 3600 combinations of opAssign. is(x.y) is 
> there just to check for the existence of a field y in x.

Thanks for the great post! Your pixAssign function is a great example and helped
me better understand static if, is and auto. It might take awhile before I can 
see why there would be trouble with trying to use a mixin to avoid paramatized 
calls to opAssign.