On Behalf Of Aleksey Gurtovoy

Brian Braatz writes:

...

Either something strange is happening with arg<> and transform or I did not write this code correctly. ( :) )

The latter :). By requesting '::type' on a metafunction you are immediately instantiating it with the placeholder argument(s), which is not what you want. Try

typedef mpl::transform< vec_t , mpl::if_< , boost::is_same<mpl::_1, A> , YES< mpl::_1 > , NO< mpl::_1 > > >::type result;

[Brian Braatz Writes:] THANK YOU - This is very helpful (in many ways) :)