Why does opDispatch not forward to operators?

[John Colvin]

On Wednesday, 7 August 2013 at 21:08:24 UTC, Tobias Pankrath 
wrote:
> import std.stdio;
>
> struct ArrayTypeA {
>         int[12] data;
>         size_t length() { return 12; }
>         auto opSlice(size_t s, size_t e) { return data[s .. e]; 
> }
> }
>
> struct ArrayTypeB {
>         int[24] data;
>
>         auto opSlice(size_t s, size_t e) { return data[s..  e]; 
> }
>         size_t length() { return 24; }
> }
>
> struct Array
> {
>         union {
>                 ArrayTypeA a = ArrayTypeA.init;
>                 ArrayTypeB b;
>         }
>         bool isA = true;
>         auto opDispatch(string s, T...)(T args)
>         {
>                 if(isA)
>                         return __traits(getMember, a, s)(args);
>                 else
>                         return __traits(getMember, b, s)(args);
>         }
> }
>
> void main() {
>
>         Array ar;
>         writeln(ar.length); // compiles
>
>          writeln(ar[3 .. 5]); // does not
>         // /tmp/test.d(37): Error: Array cannot be sliced with 
> []
> }
>
> I'd say, if something rewrites to MyType.opSlice than it's a 
> case for opDispatch, too.

I wish it did too, but apparently there is a reason why not. I 
can't remember what I was told off the top of my head, but I 
remember not being 100% convinced.

It would greatly simplify writing some wrapper types.