/*
* Copyright (c) Facebook, Inc. and its affiliates.
*
* 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 <initializer_list>
#include <iterator>
/**
* include or backport:
* * std::size
* * std::empty
* * std::data
#if __cpp_lib_nonmember_container_access >= 201411 || _MSC_VER
namespace folly {
/* using override */ using std::data;
/* using override */ using std::empty;
/* using override */ using std::size;
} // namespace folly
#else
// mimic: std::size, C++17
template <typename C>
constexpr auto size(C const& c) -> decltype(c.size()) {
return c.size();
}
template <typename T, std::size_t N>
constexpr std::size_t size(T const (&)[N]) noexcept {
return N;
// mimic: std::empty, C++17
constexpr auto empty(C const& c) -> decltype(c.empty()) {
return c.empty();
constexpr bool empty(T const (&)[N]) noexcept {
// while zero-length arrays are not allowed in the language, some compilers
// may permit them in some cases
return N == 0;
template <typename E>
constexpr bool empty(std::initializer_list<E> il) noexcept {
return il.size() == 0;
// mimic: std::data, C++17
constexpr auto data(C& c) -> decltype(c.data()) {
return c.data();
constexpr auto data(C const& c) -> decltype(c.data()) {
constexpr T* data(T (&a)[N]) noexcept {
return a;
constexpr E const* data(std::initializer_list<E> il) noexcept {
return il.begin();
#endif