20 General utilities library [utilities]

An exception of type bad_function_call is thrown by function::operator() ([func.wrap.func.inv]) when the function wrapper object has no target.

namespace std {
  class bad_function_call : public std::exception {
  public:
    // [func.wrap.badcall.const], constructor:
    bad_function_call() noexcept;
  };
} // namespace std