CallableTraits is a standalone C++11 header-only library for the inspection, synthesis, and decomposition of callable types. Language features added in later C++ standards are also supported.
The latest documentation is available here.
CallableTraits is released as part of the Boost C++ Libraries. Since it only depends on the standard library headers, you can also download it as a standalone library here.
Licensed under the Boost Software License, Version 1.0.