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

From: Robert Dailey (rcdailey_at_[hidden])
Date: 2008-03-24 16:50:29

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_at_[hidden]>
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_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.
> >
> > _______________________________________________
> > Boost-users mailing list
> > Boost-users_at_[hidden]
> > http://lists.boost.org/mailman/listinfo.cgi/boost-users
> >
>
>
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