metaprogramming question

[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);

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