Re: [Boost-users] [MPL] at<> function with too many arguments

Subject: Re: [Boost-users] [MPL] at<> function with too many arguments
From: Ryan (mccorywork_at_[hidden])
Date: 2009-09-24 21:16:23

On Mon, Aug 31, 2009 at 7:47 PM, Ryan McConnehey <mccorywork_at_[hidden]>wrote:

> I have a mpl::map as follows, with a template parameter of a passed in type
> and a template parameter of "supported_type" that is a class.
>
> using boost::mpl;
> enum { value = 1 + supported_type::value };
> typedef typename insert<typename supported_type::type_map, pair<T,
> int_<value> > >::type  type_map;
>
> I'm trying to create a function that searches the map for a given type and
> returns a numeric value if it's found or -1 if it's not found.
>
> template <typename S>  int typeValue(void)  {
>  return at< type_map, S, int_<-1> >::type::value;
> }
>
> The documentation says I can specify a default value for "at" that is
> returned if the given key isn't found.  The compiler, though, says that I've
> provided too many arguments.  Have I called "at" incorrectly?  Is the
> documentation incorrect?  Is the fault with the compiler (VS 2005)?
>
> Ryan
>

I've created a work around using the boost::enable_if and boost::disable_if
that provides the functionality I need.  I would prefer to use the mpl::at
with the default argument if I can.  If someone could help me I'd appreciate
it.

template <typename S> typename boost::enable_if< boost::mpl::has_key<
type_map, S >, int >::type typeValue(void)  {
  return boost::mpl::at< type_map, S >::type::value;
}

template <typename S> typename boost::disable_if< boost::mpl::has_key<
type_map, S >, int >::type typeValue(void)  {
  return -1;
}

Ryan