Re: [Boost-users] [enable_if] Type choices

From: Ovanes Markarian (om_boost_at_[hidden])
Date: 2008-03-24 16:32:33

Hi!

Using mpl in your case is not a lot of work ;) Just use the mpl::set for the
set of accepted types and the mpl::has_key meta-function in conjunction with
enable_if.

//////////// UNTESTED CODE ////////////////////

#include <boost/utility/enable_if.hpp>
#include <boost/mpl/set.hpp>
#include <boost/mpl/has_key.hpp>

....

typedef set< char,wchar_t>  accepted_types;

template<class T>
void foo( T t
           , typename
               boost::enable_if
               <
                  typename
                    boost::mpl::has_key<accepted_types, T>::type
               >::type* reserved=0
            )
{
    ...
}

/////////////// END OF UNTESTED CODE ////////////////

Good Luck,
Ovanes

On 3/24/08, Robert Dailey <rcdailey_at_[hidden]> wrote:
>
> Hi,
>
> I have a simple template function that takes one argument. For example:
>
> template< typename t_type >
> void foo( t_type param )
> {
> }
>
>
> I want to restrict the type of t_type to a certain subset of types, such
> as 'char' or 'wchar_t'. If the user passes in any type other than those two
> types, the compiler should not be able to find an overload for foo() that
> matches the argument types. Note that I would also be using boost::enable_if
> to test this condition, however I do not see anything in type_traits or
> anywhere else to perform such a test.
>
> I thought of using mpl::vector to create a list of types the function
> would take and using enable_if to check if the type is in the container, but
> this seems like a lot of work. I want to see if there is a simpler, more
> compact solution.
>
> Thanks.
>
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