[func.wrap.func.targ]
22 General utilities library [utilities]
22.10 Function objects [function.objects]
22.10.17 Polymorphic function wrappers [func.wrap]
22.10.17.3 Class template function [func.wrap.func]
22.10.17.3.6 Target access [func.wrap.func.targ]
const type_info& target_type() const noexcept;
template<class T> T* target() noexcept;
template<class T> const T* target() const noexcept;