Angus Leeming <angus.leeming@btopenworld.com> 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<state, state2, state3> , N >::type >::type*=0 ); where template <class S, class N> struct contains_c : mpl::not_< mpl::is_same< typename mpl::find_if<S,mpl::equal_to<N,_> >::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