I was trying to use mpl::contains with list_c and it always seems to return mpl::false_.

For example typedef mpl::list_c< int ,16,8 > mylist; typedef mpl::contains<mylist, mpl::int_<16> >::type tt;

I've run into this issue in the past as well, and I vaguely rememember seeing mpl::integral_c<long>'s being used somewhere along the way, instead of mpl::integral_c<int>'s as one would expect. I'm not sure if that is still the case, or whether I was decaffeinated, but I ended up fixing it by using the following work-around (pseudo-code): template<class Sequence, class Elem> struct contains : mpl::contains < Sequence, mpl::integral_c < mpl::front<Sequence>::value_type, Elem::value> > >{}; Which isn't pretty, but it got the job done. You basically get the value_type of the first element in the sequence, to make sure the base type of the integral_c you're looking for matches with the sequence. I'm hoping Alexsey or Dave will step in here and clarify this, as it has been a source of confusion for me as well. Regards, Jaap Suter