Invoke.h

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/*
 * Copyright 2017-present Facebook, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#pragma once

#include <functional>
#include <type_traits>

#include <folly/Preprocessor.h>
#include <folly/Traits.h>

#if __cpp_lib_invoke >= 201411 || _MSC_VER

namespace folly {

/* using override */ using std::invoke;
}

#else

namespace folly {

//  mimic: std::invoke, C++17
template <typename F, typename... Args>
constexpr auto invoke(F&& f, Args&&... args) noexcept(
    noexcept(static_cast<F&&>(f)(static_cast<Args&&>(args)...)))
    -> decltype(static_cast<F&&>(f)(static_cast<Args&&>(args)...)) {
  return static_cast<F&&>(f)(static_cast<Args&&>(args)...);
}
template <typename M, typename C, typename... Args>
constexpr auto invoke(M(C::*d), Args&&... args)
    -> decltype(std::mem_fn(d)(static_cast<Args&&>(args)...)) {
  return std::mem_fn(d)(static_cast<Args&&>(args)...);
}

} // namespace folly

#endif

// Only available in >= MSVC 2017 15.3 in C++17
#if __cpp_lib_is_invocable >= 201703 || \
    (_MSC_VER >= 1911 && _MSVC_LANG > 201402)

namespace folly {

/* using override */ using std::invoke_result;
/* using override */ using std::invoke_result_t;
/* using override */ using std::is_invocable;
/* using override */ using std::is_invocable_r;
/* using override */ using std::is_nothrow_invocable;
/* using override */ using std::is_nothrow_invocable_r;

} // namespace folly

#else

namespace folly {

namespace invoke_detail {

template <typename F, typename... Args>
using invoke_result_ =
    decltype(invoke(std::declval<F>(), std::declval<Args>()...));

template <typename F, typename... Args>
struct invoke_nothrow_
    : bool_constant<noexcept(
          invoke(std::declval<F>(), std::declval<Args>()...))> {};

//  from: http://en.cppreference.com/w/cpp/types/result_of, CC-BY-SA

template <typename Void, typename F, typename... Args>
struct invoke_result {};

template <typename F, typename... Args>
struct invoke_result<void_t<invoke_result_<F, Args...>>, F, Args...> {
  using type = invoke_result_<F, Args...>;
};

template <typename Void, typename F, typename... Args>
struct is_invocable : std::false_type {};

template <typename F, typename... Args>
struct is_invocable<void_t<invoke_result_<F, Args...>>, F, Args...>
    : std::true_type {};

template <typename Void, typename R, typename F, typename... Args>
struct is_invocable_r : std::false_type {};

template <typename R, typename F, typename... Args>
struct is_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...>
    : std::is_convertible<invoke_result_<F, Args...>, R> {};

template <typename Void, typename F, typename... Args>
struct is_nothrow_invocable : std::false_type {};

template <typename F, typename... Args>
struct is_nothrow_invocable<void_t<invoke_result_<F, Args...>>, F, Args...>
    : invoke_nothrow_<F, Args...> {};

template <typename Void, typename R, typename F, typename... Args>
struct is_nothrow_invocable_r : std::false_type {};

template <typename R, typename F, typename... Args>
struct is_nothrow_invocable_r<void_t<invoke_result_<F, Args...>>, R, F, Args...>
    : StrictConjunction<
          std::is_convertible<invoke_result_<F, Args...>, R>,
          invoke_nothrow_<F, Args...>> {};

} // namespace invoke_detail

//  mimic: std::invoke_result, C++17
template <typename F, typename... Args>
struct invoke_result : invoke_detail::invoke_result<void, F, Args...> {};

//  mimic: std::invoke_result_t, C++17
template <typename F, typename... Args>
using invoke_result_t = typename invoke_result<F, Args...>::type;

//  mimic: std::is_invocable, C++17
template <typename F, typename... Args>
struct is_invocable : invoke_detail::is_invocable<void, F, Args...> {};

//  mimic: std::is_invocable_r, C++17
template <typename R, typename F, typename... Args>
struct is_invocable_r : invoke_detail::is_invocable_r<void, R, F, Args...> {};

//  mimic: std::is_nothrow_invocable, C++17
template <typename F, typename... Args>
struct is_nothrow_invocable
    : invoke_detail::is_nothrow_invocable<void, F, Args...> {};

//  mimic: std::is_nothrow_invocable_r, C++17
template <typename R, typename F, typename... Args>
struct is_nothrow_invocable_r
    : invoke_detail::is_nothrow_invocable_r<void, R, F, Args...> {};

} // namespace folly

#endif

namespace folly {
namespace detail {

struct invoke_private_overload;

template <typename Invoke>
struct free_invoke_proxy {
 public:
  template <typename... Args>
  struct invoke_result : folly::invoke_result<Invoke, Args...> {};
  template <typename... Args>
  using invoke_result_t = folly::invoke_result_t<Invoke, Args...>;
  template <typename... Args>
  struct is_invocable : folly::is_invocable<Invoke, Args...> {};
  template <typename R, typename... Args>
  struct is_invocable_r : folly::is_invocable_r<R, Invoke, Args...> {};
  template <typename... Args>
  struct is_nothrow_invocable : folly::is_nothrow_invocable<Invoke, Args...> {};
  template <typename R, typename... Args>
  struct is_nothrow_invocable_r
      : folly::is_nothrow_invocable_r<R, Invoke, Args...> {};

  template <typename... Args>
  static constexpr auto invoke(Args&&... args) noexcept(
      noexcept(Invoke{}(static_cast<Args&&>(args)...)))
      -> decltype(Invoke{}(static_cast<Args&&>(args)...)) {
    return Invoke{}(static_cast<Args&&>(args)...);
  }

  using invoke_type = Invoke;
};

} // namespace detail
} // namespace folly

/***
 *  FOLLY_CREATE_FREE_INVOKE_TRAITS
 *
 *  Used to create traits container, bound to a specific free-invocable name,
 *  with the following member traits types and aliases:
 *
 *  * invoke_result
 *  * invoke_result_t
 *  * is_invocable
 *  * is_invocable_r
 *  * is_nothrow_invocable
 *  * is_nothrow_invocable_r
 *
 *  The container also has a static member function:
 *
 *  * invoke
 *
 *  And a member type alias:
 *
 *  * invoke_type
 *
 *  These members have behavior matching the behavior of C++17's corresponding
 *  invocation traits types, aliases, and functions, but substituting canonical
 *  invocation with member invocation.
 *
 *  Example:
 *
 *    FOLLY_CREATE_FREE_INVOKE_TRAITS(foo_invoke_traits, foo);
 *
 *  The traits container type `foo_invoke_traits` is generated in the current
 *  namespace and has the listed member types and aliases. They may be used as
 *  follows:
 *
 *    namespace Deep {
 *    struct CanFoo {};
 *    int foo(CanFoo const&, Bar&) { return 1; }
 *    int foo(CanFoo&&, Car&&) noexcept { return 2; }
 *    }
 *
 *    using traits = foo_invoke_traits;
 *
 *    traits::invoke(Deep::CanFoo{}, Car{}) // 2
 *
 *    traits::invoke_result<Deep::CanFoo, Bar&> // has member
 *    traits::invoke_result_t<Deep::CanFoo, Bar&> // int
 *    traits::invoke_result<Deep::CanFoo, Bar&&> // empty
 *    traits::invoke_result_t<Deep::CanFoo, Bar&&> // error
 *
 *    traits::is_invocable<CanFoo, Bar&>::value // true
 *    traits::is_invocable<CanFoo, Bar&&>::value // false
 *
 *    traits::is_invocable_r<int, CanFoo, Bar&>::value // true
 *    traits::is_invocable_r<char*, CanFoo, Bar&>::value // false
 *
 *    traits::is_nothrow_invocable<CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<CanFoo, Car&&>::value // true
 *
 *    traits::is_nothrow_invocable<int, CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<char*, CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<int, CanFoo, Car&&>::value // true
 *    traits::is_nothrow_invocable<char*, CanFoo, Car&&>::value // false
 *
 *  When a name has a primary definition in a fixed namespace and alternate
 *  definitions in the namespaces of its arguments, the primary definition may
 *  automatically be found as follows:
 *
 *    FOLLY_CREATE_FREE_INVOKE_TRAITS(swap_invoke_traits, swap, std);
 *
 *  In this case, `swap_invoke_traits::invoke(int&, int&)` will use the primary
 *  definition found in `namespace std` relative to the current namespace, which
 *  may be equivalent to `namespace ::std`. In contrast:
 *
 *    namespace Deep {
 *    struct HasData {};
 *    void swap(HasData&, HasData&) { throw 7; }
 *    }
 *
 *    using traits = swap_invoke_traits;
 *
 *    HasData a, b;
 *    traits::invoke(a, b); // throw 7
 */
#define FOLLY_CREATE_FREE_INVOKE_TRAITS(classname, funcname, ...)    \
  namespace classname##__folly_detail_invoke_ns {                    \
    namespace classname##__folly_detail_invoke_ns_inline {           \
      FOLLY_PUSH_WARNING                                             \
      FOLLY_CLANG_DISABLE_WARNING("-Wunused-function")               \
      void funcname(::folly::detail::invoke_private_overload&);      \
      FOLLY_POP_WARNING                                              \
    }                                                                \
    using FB_ARG_2_OR_1(                                             \
        classname##__folly_detail_invoke_ns_inline                   \
            FOLLY_PP_DETAIL_APPEND_VA_ARG(__VA_ARGS__))::funcname;   \
    struct classname##__folly_detail_invoke {                        \
      template <typename... Args>                                    \
      constexpr auto operator()(Args&&... args) const                \
          noexcept(noexcept(funcname(static_cast<Args&&>(args)...))) \
              -> decltype(funcname(static_cast<Args&&>(args)...)) {  \
        return funcname(static_cast<Args&&>(args)...);               \
      }                                                              \
    };                                                               \
  }                                                                  \
  struct classname : ::folly::detail::free_invoke_proxy<             \
                         classname##__folly_detail_invoke_ns::       \
                             classname##__folly_detail_invoke> {}

namespace folly {
namespace detail {

template <typename Invoke>
struct member_invoke_proxy {
 public:
  template <typename O, typename... Args>
  struct invoke_result : folly::invoke_result<Invoke, O, Args...> {};
  template <typename O, typename... Args>
  using invoke_result_t = folly::invoke_result_t<Invoke, O, Args...>;
  template <typename O, typename... Args>
  struct is_invocable : folly::is_invocable<Invoke, O, Args...> {};
  template <typename R, typename O, typename... Args>
  struct is_invocable_r : folly::is_invocable_r<R, Invoke, O, Args...> {};
  template <typename O, typename... Args>
  struct is_nothrow_invocable
      : folly::is_nothrow_invocable<Invoke, O, Args...> {};
  template <typename R, typename O, typename... Args>
  struct is_nothrow_invocable_r
      : folly::is_nothrow_invocable_r<R, Invoke, O, Args...> {};

  template <typename O, typename... Args>
  static constexpr auto invoke(O&& o, Args&&... args) noexcept(
      noexcept(Invoke{}(static_cast<O&&>(o), static_cast<Args&&>(args)...)))
      -> decltype(Invoke{}(static_cast<O&&>(o), static_cast<Args&&>(args)...)) {
    return Invoke{}(static_cast<O&&>(o), static_cast<Args&&>(args)...);
  }

  using invoke_type = Invoke;
};

} // namespace detail
} // namespace folly

/***
 *  FOLLY_CREATE_MEMBER_INVOKE_TRAITS
 *
 *  Used to create traits container, bound to a specific member-invocable name,
 *  with the following member traits types and aliases:
 *
 *  * invoke_result
 *  * invoke_result_t
 *  * is_invocable
 *  * is_invocable_r
 *  * is_nothrow_invocable
 *  * is_nothrow_invocable_r
 *
 *  The container also has a static member function:
 *
 *  * invoke
 *
 *  And a member type alias:
 *
 *  * invoke_type
 *
 *  These members have behavior matching the behavior of C++17's corresponding
 *  invocation traits types, aliases, and functions, but substituting canonical
 *  invocation with member invocation.
 *
 *  Example:
 *
 *    FOLLY_CREATE_MEMBER_INVOKE_TRAITS(foo_invoke_traits, foo);
 *
 *  The traits container type `foo_invoke_traits` is generated in the current
 *  namespace and has the listed member types and aliases. They may be used as
 *  follows:
 *
 *    struct CanFoo {
 *      int foo(Bar&) { return 1; }
 *      int foo(Car&&) noexcept { return 2; }
 *    };
 *
 *    using traits = foo_invoke_traits;
 *
 *    traits::invoke(CanFoo{}, Car{}) // 2
 *
 *    traits::invoke_result<CanFoo, Bar&> // has member
 *    traits::invoke_result_t<CanFoo, Bar&> // int
 *    traits::invoke_result<CanFoo, Bar&&> // empty
 *    traits::invoke_result_t<CanFoo, Bar&&> // error
 *
 *    traits::is_invocable<CanFoo, Bar&>::value // true
 *    traits::is_invocable<CanFoo, Bar&&>::value // false
 *
 *    traits::is_invocable_r<int, CanFoo, Bar&>::value // true
 *    traits::is_invocable_r<char*, CanFoo, Bar&>::value // false
 *
 *    traits::is_nothrow_invocable<CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<CanFoo, Car&&>::value // true
 *
 *    traits::is_nothrow_invocable<int, CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<char*, CanFoo, Bar&>::value // false
 *    traits::is_nothrow_invocable<int, CanFoo, Car&&>::value // true
 *    traits::is_nothrow_invocable<char*, CanFoo, Car&&>::value // false
 */
#define FOLLY_CREATE_MEMBER_INVOKE_TRAITS(classname, membername)              \
  struct classname##__folly_detail_member_invoke {                            \
    template <typename O, typename... Args>                                   \
    constexpr auto operator()(O&& o, Args&&... args) const noexcept(noexcept( \
        static_cast<O&&>(o).membername(static_cast<Args&&>(args)...)))        \
        -> decltype(                                                          \
            static_cast<O&&>(o).membername(static_cast<Args&&>(args)...)) {   \
      return static_cast<O&&>(o).membername(static_cast<Args&&>(args)...);    \
    }                                                                         \
  };                                                                          \
  struct classname : ::folly::detail::member_invoke_proxy<                    \
                         classname##__folly_detail_member_invoke> {}