[boost] How can I detect if a template static member function exists?

I'd like to write a trait: template<class T> struct has_content_length : std::integral_constant{}; which detects whether or not a template static member function is present in T. Here's a typical T: struct X { template static std::uint64_t content_length( message const& m); }; How can I detect if X::content_length(m) is callable for any m of type message template?