[boost] [type_erasure]

Hi, I am trying to use Boost.TypeErasure library with a 'concept' that provides contextual conversion to *bool*. That is, I want to type-erase types that provide the following operations for some invented object *o*: * if (o) {}* * if (!o) {}* * bool (o); * I cannot find a predefined concept for that, nor can I use BOOST_TYPE_ERASURE_MEMBER or BOOST_TYPE_ERASURE_FREE, because that will not work for built in types. Is there any convenience tool that enables specifying such concept? Regards, &rzej