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

[Walter Bright]

I wrote that a very long time ago, and don't remember the details.

David Simcha wrote:
> 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
>
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