ceph/src/rocksdb/third-party/folly/folly/functional/Invoke.h

   1 //  Copyright (c) 2011-present, Facebook, Inc.  All rights reserved.
   2 //  This source code is licensed under both the GPLv2 (found in the
   3 //  COPYING file in the root directory) and Apache 2.0 License
   4 //  (found in the LICENSE.Apache file in the root directory).
   5
   6 #pragma once
   7
   8 #include <folly/Traits.h>
   9
  10 #include <functional>
  11 #include <type_traits>
  12
  13 namespace folly {
  14 namespace invoke_detail {
  15 template <typename F, typename... Args>
  16 using invoke_result_ = decltype(std::declval<F>()(std::declval<Args>()...));
  17
  18 template <typename Void, typename F, typename... Args>
  19 struct is_invocable : std::false_type {};
  20
  21 template <typename F, typename... Args>
  22 struct is_invocable<void_t<invoke_result_<F, Args...>>, F, Args...>
  23     : std::true_type {};
  24
  25 template <typename Void, typename R, typename F, typename... Args>
  26 struct is_invocable_r : std::false_type {};
  27
  28 template <typename R, typename F, typename... Args>
  29 struct is_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...>
  30     : std::is_convertible<invoke_result_<F, Args...>, R> {};
  31 } // namespace invoke_detail
  32
  33 //  mimic: std::is_invocable, C++17
  34 template <typename F, typename... Args>
  35 struct is_invocable : invoke_detail::is_invocable<void, F, Args...> {};
  36
  37 //  mimic: std::is_invocable_r, C++17
  38 template <typename R, typename F, typename... Args>
  39 struct is_invocable_r : invoke_detail::is_invocable_r<void, R, F, Args...> {};
  40 } // namespace folly