[dmd-internals] opApply with alias instead of delegate?

[David Simcha]

I found this goodie in opover.c of the DMD source, and am wondering 
if/when it will be implemented fully.  I think that opApply with an 
alias instead of a delegate would be a great thing to have, rather than 
having to rely on a "sufficiently smart compiler" to inline delegates 
for opApply (LDC does this sometimes, though not very reliably) or not 
being able to use opApply in ultra performance-critical situations 
(status quo with DMD).  Is there any fundamental reason design reason 
why this didn't work out, or is it just yet another low-priority todo?

/*******************************************
  * Infer foreach arg types from a template function opApply which looks 
like:
  *    int opApply(alias int func(ref uint))() { ... }
  */

#if 0
void inferApplyArgTypesZ(TemplateDeclaration *tstart, Parameters *arguments)
{
     for (TemplateDeclaration *td = tstart; td; td = td->overnext)
     {
         if (!td->scope)
         {
             error("forward reference to template %s", td->toChars());
             return;
         }
         if (!td->onemember || 
!td->onemember->toAlias()->isFuncDeclaration())
         {
             error("is not a function template");
             return;
         }
         if (!td->parameters || td->parameters->dim != 1)
             continue;
         TemplateParameter *tp = (TemplateParameter 
*)td->parameters->data[0];
         TemplateAliasParameter *tap = tp->isTemplateAliasParameter();
         if (!tap || !tap->specType || tap->specType->ty != Tfunction)
             continue;
         TypeFunction *tf = (TypeFunction *)tap->specType;
         if (inferApplyArgTypesY(tf, arguments) == 0)    // found it
             return;
     }
}
#endif