A possible solution for the opIndexXxxAssign morass

[Bill Baxter]

On Tue, Oct 13, 2009 at 10:00 AM, Steven Schveighoffer
<schveiguy at yahoo.com> wrote:
> On Tue, 13 Oct 2009 12:44:21 -0400, Denis Koroskin <2korden at gmail.com>
> wrote:
>
>> Another thing I dislike about this proposal is that "a[b] += c;"
>> translates into "opAddAssign" and doesn't mention "index" while "a[b] = c;"
>> does ("opIndexAssign").
>
> I think the optimization translates to opAssign as well:
>
> a[b] = c; => a.opAssign(b, c);
>
> On Tue, 13 Oct 2009 12:37:50 -0400, Bill Baxter <wbaxter at gmail.com> wrote:
>
>> Huh? It didn't sound to me like it would get rid of anything, except
>> for the use of the word "index" in many methods that have to do with
>> index operations.  That just seems confusing to me.   I think the
>> opIndexXxxAssign functions may need to be added, but adding them by
>> overloading existing names doesn't seem a win to me.
>
> The point is to avoid having operator function names multiply out of
> control.  Re-examining it, I agree with you -- It makes little sense to have
> an operator that involves an indexing lack the term Index.
>
> If only there was a way to make the indexing orthogonal to the other
> operation.  For example something like:
>
> struct X
> {
>   private int[] arr;
>   opIndex(int idx) // declares a new "namespace" where idx is an implicitly
> passed argument
>   {
>      int opAssign(int x)
>      {
>         arr[idx] = x;
>         return x;
>      }
>   }
> }
>
> I know this probably doesn't parse well, should opIndex be a keyword? or an
> attribute?

I don't think the number of /names/ required is the problem.  It's
just the sheer number of functions themselves that's the issue.  I
think a lot of that could mostly be fixed by some smart macros.   And
until they exist, mixins can help.

struct Vec
{
    float x,y,z;
mixin(implementOperators("+ - / * += -= /= *=",
     q{
           a.x op= b.x;
           a.y op= b.y;
           a.z op= b.z;
     });
}

The code gives a list of operators to implement and one prototypical
op= body.  With a smart enough CTFE string function that's all you
need to generate all the listed operators.  Not sure how to work index
operators into that.

--bb