metaprogramming question

[BCS]

Hello Justin Spahr-Summers,

> On Mon, 19 Apr 2010 00:12:28 +0000 (UTC), Graham Fawcett
> <fawcett at uwindsor.ca> wrote:
> 
>> Hi folks,
>> 
>> I'd like to wrap a family of C functions that look like this:
>> 
>> gboolean fooXXX(arg1, ..., argN, GError** err)
>> 
>> Their signatures and arities vary, but they all have a GError** as
>> their last argument. If a function returns false, then 'err' will be
>> set to a relevant Error struct.
>> 
>> I would like to write a wrapper that would let me call these
>> functions sort of like this:
>> 
>> check!(fooXXX(arg1, ..., argN))
>> 
>> where the 'check' expression would be equivalent to:
>> 
>> GError* err;
>> bool ok = fooXXX(arg1, ..., argN, &err);
>> if (!ok)
>> throw new Exception((*err).message);
>> Does D (2.0) offer a metaprogramming technique I could use to
>> accomplish this -- particularly, to inject that 'err' argument into
>> the tail of the fooXXX call?
>> 
>> Thanks,
>> Graham
> You can use some expression tuple magic to accomplish something like
> that:
> 
> bool check(alias func, EL ...)() {
> GError* err;
> bool ok = func(EL, &err);
> if (!ok)
> throw new Exception((*err).message);
> return ok;
> }
> // used like:
> check!(fooXXX, arg1, ..., argN);

IIRC that should be:

check!(fooXXX, argType1, ..., argTypeN)(arg1, ..., argN);

> See http://digitalmars.com/d/2.0/template.html#TemplateTupleParameter
> 

Or you can mangel that a bit:

template check(alias func) {
   bool check(EL ...)() {
      GError* err;
      bool ok = func(EL, &err);
      if (!ok)
         throw new Exception((*err).message);
      return ok;
   }
}

that should allow you to call it like:

check!(fooXXX)(arg1, ..., argN);

-- 
... <IXOYE><