[Boost-users] Re: enable_if and constructors

Angus Leeming writes:

Is it possible to use enable_if with a constructor?

In principle, yes. You just add a dummy default parameter for the enabler.

For example, I'd like to define a constructor that allows only certain values of an enum:

No chance; that's a runtime test... or you'd have to specify the enum as a template argument to the ctor explicitly... but you can't provide explicit template arguments to ctors. Well, you can do something like: template <class N> foo( N , typename boost::enable_if< typename contains_c< mpl::vector_c , N >::type >::type*=0 ); where template struct contains_c : mpl::not_< mpl::is_same< typename mpl::find_if >::type , typename mpl::end<S>::type > > {}; and then a foo is constructed something like this: foo x( mpl::int_<state2>() ); HTH, -- Dave Abrahams Boost Consulting www.boost-consulting.com