lambda_to_function_without_specify_type.cpp

namespace detail {
  template <typename Res, typename... Args>
  Obj<Res, Args...> NewObj(std::function<Res(Args...)>&& func) {
      return std::make_shared<Obj<Res(Args...)>>(std::forward<std::function<Res(Args...)>&&>(func));
  }
}

namespace detail {
  template <typename F>
  struct function_traits : public function_traits<decltype(&std::decay<F>::type::operator())> {};

  template <typename R, typename C, typename... Args>
  struct function_traits<R (C::*)(Args...) const> {
      using function_type = std::function<R(Args...)>;
  };
  // support mutable lambda object
  template <typename R, typename C, typename... Args>
  struct function_traits<R (C::*)(Args...)> {
      using function_type = std::function<R(Args...)>;
  };

}  // namespace detail

template <typename F>
using function_type_t = typename detail::function_traits<F>::function_type;

template <typename F>
function_type_t<F> to_function(F&& lambda) {
    return static_cast<function_type_t<F>>(std::forward<F>(lambda));
}

template <typename Closure>
auto NewObj(Closure&& closure) {
    return detail::NewObj(to_function(std::forward<Closure>(closure)));
}