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/**
* Copyright (C) 2022-present MongoDB, Inc.
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the Server Side Public License, version 1,
* as published by MongoDB, Inc.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* Server Side Public License for more details.
*
* You should have received a copy of the Server Side Public License
* along with this program. If not, see
* <http://www.mongodb.com/licensing/server-side-public-license>.
*
* As a special exception, the copyright holders give permission to link the
* code of portions of this program with the OpenSSL library under certain
* conditions as described in each individual source file and distribute
* linked combinations including the program with the OpenSSL library. You
* must comply with the Server Side Public License in all respects for
* all of the code used other than as permitted herein. If you modify file(s)
* with this exception, you may extend this exception to your version of the
* file(s), but you are not obligated to do so. If you do not wish to do so,
* delete this exception statement from your version. If you delete this
* exception statement from all source files in the program, then also delete
* it in the license file.
*/
#pragma once
#include <boost/optional.hpp>
#include <optional>
#include <ostream>
#include <string>
#include <type_traits>
#include "mongo/stdx/type_traits.h"
namespace mongo {
template <typename T>
inline constexpr bool isBoostOptional = false;
template <typename... Ts>
inline constexpr bool isBoostOptional<boost::optional<Ts...>> = true;
template <typename T>
inline constexpr bool isStdOptional = false;
template <typename... Ts>
inline constexpr bool isStdOptional<std::optional<Ts...>> = true; // NOLINT
/**
* Some utilities for formatting optional<T> values, (either std or boost).
* Meant as a substitute for boost/optional_io.hpp.
*/
namespace optional_io {
template <typename T>
using CanStreamOp = decltype(std::declval<std::ostream&>() << std::declval<const T&>());
template <typename T>
inline constexpr bool canStream = stdx::is_detected_v<CanStreamOp, T>;
/**
* True if `Extension<T>` is supported. Cumbersome, but this set of
* specializations is necessary because `boost::optional<T>` defines a
* SFINAE-hostile `operator<<`.
*/
template <typename T>
inline constexpr bool canStreamWithExtension = canStream<T>;
template <>
inline constexpr bool canStreamWithExtension<std::nullopt_t> = true; // NOLINT
template <typename T>
inline constexpr bool canStreamWithExtension<std::optional<T>> = // NOLINT
canStreamWithExtension<T>;
template <>
inline constexpr bool canStreamWithExtension<boost::none_t> = true;
template <typename T>
inline constexpr bool canStreamWithExtension<boost::optional<T>> = canStreamWithExtension<T>;
namespace detail {
/**
* The `stream` overloads provide the same formatting as boost/optional_io.hpp,
* but support both the `boost` and `std` optional types.
*/
template <typename T, std::enable_if_t<canStream<T>, int> = 0>
std::ostream& stream(std::ostream& os, const T& v) {
return os << v;
}
inline std::ostream& stream(std::ostream& os, std::nullopt_t) { // NOLINT
return os << "--";
}
template <typename T, std::enable_if_t<canStreamWithExtension<T>, int> = 0>
std::ostream& stream(std::ostream& os, const std::optional<T>& v) { // NOLINT
if (!v)
return stream(os, std::nullopt);
return stream(os << " ", *v);
}
inline std::ostream& stream(std::ostream& os, boost::none_t) {
return os << "--";
}
template <typename T, std::enable_if_t<canStreamWithExtension<T>, int> = 0>
std::ostream& stream(std::ostream& os, const boost::optional<T>& v) {
if (!v)
return stream(os, std::nullopt);
return stream(os << " ", *v);
}
} // namespace detail
/**
* Streamable wrapper for an object reference.
* This object formats just like the object it refers to.
*
* But if the object happens to be an optional, then the wrapper will be
* streamble in the `boost/optional_io.hpp` formatting style. That is, non-empty
* optionals are formatted with a space followed by the value's representation.
* Empty optionals are "--".
*
* Example:
* std::cout << Extension{someOptional};
* std::cout << Extension{123};
*/
template <typename T, std::enable_if_t<canStreamWithExtension<T>, int> = 0>
class Extension {
public:
explicit Extension(const T& v) : v{v} {}
private:
friend std::ostream& operator<<(std::ostream& os, const Extension& o) {
return detail::stream(os, o.v);
}
const T& v;
};
template <typename T, std::enable_if_t<canStreamWithExtension<T>, int> = 0>
Extension(const T& t)->Extension<T>;
} // namespace optional_io
} // namespace mongo
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