Based on your and Vicente's input, I'll remove static_assert from contracts (pre, post, inv, etc).
Is any predicate programmable with static_assert also programmable with Boost.ConceptCheck? I guess so if the Boost.ConceptCheck concept can do the static assertion using Boost.MPL or Boost.StaticAssert. If that it true then no need for me to provide static_assert at all, just use Boost.ConceptCheck. Otherwise, I'll allow static_assert together with Boost.ConceptCheck concepts in the requires clausle. How does that sound?
I do not know if Boost.ConceptCheck offers the capability of verifying any boolean predicate. I know that concepts proposal (N2081) offered a special concept True for that purpose (not sure if it is definable in Boost.ConceptCheck). As a side note, in the new attempt at concept design described in N3331, any concept is a boolean predicate by definition; thus you can constraint template like this: template <typename T> requires InputIterator<T> && sizeof(T) > sizeof(void*) ... I believe that whatever the answer to your question is, your idea to enable static asserts along concept checking adds some value (let others judge ho much): with concept checks you can only eliminate your template (or template specialization) from overload resolution set and see what happens: perhaps another overload will be picked and the compilation will succeed. With static assertions, on the other hand, your template is _always_ always preferred only to trigger compilation error the second after: this is often useful when you want to provide clear error messages and you know there will be no other overload. For instance, if I write a binary number literal, and I want to specify at compile-time that my literal can only accept 0s or 1s, I would never use concepts or sfinae tricks: template <char... C> requires Only0sAnd1s<C...>::value constexpr unsigned operator "" _B(); Instead, I would prefer to write: template <char... C> constexpr unsigned operator "" _B() { static_assert( Only0sAnd1s<C...>::value, "only 0s and 1s allowed in binary literal" ); return ... } Regards, &rzej