For what it's worth, Rob's code is also valid for C++ (and Inline::CPP):

use strict;
use warnings;

use Inline CPP => Config =>
    BUILD_NOISY => 1;

use Inline CPP => <<'EOCPP';

int add(SV * a, ...) {
 dXSARGS;
 int i, ret = 0;

 for(i = 0; i < items; i++)
   ret += SvIV(ST(i));

 return ret;
}

EOCPP

print add(11, 12), "\n"; # prints 23
print add(10, 11, 12), "\n"; # prints 33
[download]

...outputs...

23
33
[download]

While that's still not the same as function overloading, It's actually one of the best (clearest) examples I've seen anywhere on how to use the "..." parameter. I might have to add it to Inline::CPP's POD on some future release.

Another approach would be to use Inline::CPP, and wrap your functions in classes:

use strict;
use warnings;

use Inline CPP => Config =>
    BUILD_NOISY => 1;

use Inline CPP => 'DATA';

my $foo = Foo->new();
my $bar = Bar->new();

sub add {
    if( @_ == 2 ) {
        return $foo->add(@_);
    }
    return $bar->add(@_);
}

__DATA__
__CPP__

struct Foo {
    add( int a, int b ) { return a + b; }
};

struct Bar {
    add( int a, int b, int c ) { return a + b + c }
};
[download]

Of course with this process you're adding an additional Perl layer, so if your C++ subs are trivial, your performance will actually go down.

As the POD for Inline::CPP states, the module enables a large subset of C++, but not all of C++. Function overloading is one of those "not all" areas.