On 3/24/08, Robert Dailey <rcdailey@gmail.com> wrote:

Thanks, mpl::set is even better, I was going to use mpl::vector, which probably wouldn't have worked.

I had a feeling the MPL library would be involved, but I wanted to make sure the type_traits library didn't already have something in place for this kind of situation. Thanks again!

On Mon, Mar 24, 2008 at 3:32 PM, Ovanes Markarian <om_boost@keywallet.com> wrote:

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@gmail.com> 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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