Re: [boost] [parameter] - catching accidental duplicate parameters at compile time

From: David Abrahams (dave_at_[hidden])
Date: 2005-11-03 17:47:32

Daniel Earwicker <daniel.earwicker_at_[hidden]> writes:

> Oooh, that's much better. With used_keywords as an empty set in
> empty_arg_list, all it needs in arg_list is:
>
>    BOOST_STATIC_ASSERT((!boost::mpl::has_key<
>            typename Next::used_keywords, key_type>::type::value));

Use BOOST_MPL_ASSERT_MSG here.

>    typedef typename mpl::insert<typename Next::used_keywords,
>            key_type>::type used_keywords;
>
> Or is there already something that captures the above pattern, i.e.
> refuses to insert a duplicate?

Not that I know of.

Actually in this case I think I'd prefer to see a solution using
overloading directly, just to cut down on instantiations.  The
arg_list, after all, is almost the same structure as the set already.
Something like:

  static char (& has_key(K const&) )[2];

  BOOST_MPL_ASSERT_MSG( 
        sizeof(Next::has_key(make<K>())) == 1
      , duplicate_keyword, (K)
  );

If you could submit a patch to the current CVS along with an
expected-compilation-failure test case, I'd be happy to apply it.

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com