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/**
* Copyright (C) 2020-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 <fmt/format.h>
#include <tuple>
#include <type_traits>
namespace mongo {
namespace logv2 {
namespace detail {
/**
* Helper to be used inside logAttrs() functions, captures rvalues by value so they don't go out of
* scope Can create a tuple of loggable named attributes for the logger
*/
template <typename... Ts>
class ComposedAttr {
public:
ComposedAttr(Ts&&... args) : _values(std::move(args)...) {}
/**
* Creates a flattend tuple of loggable named attributes
*/
auto attributes() const;
private:
std::tuple<Ts...> _values;
};
template <typename>
struct IsComposedAttr : std::false_type {};
template <typename... Ts>
struct IsComposedAttr<ComposedAttr<Ts...>> : std::true_type {};
/**
* Helper to make regular attributes composable with combine()
*/
template <typename T>
auto logAttrs(const fmt::internal::named_arg<T, char>& a) {
return a;
}
/**
* Flattens the input into a single tuple (no tuples of tuples). Passes through the input by
* reference by possible. May only be used at the call side of the log system to avoid dangling
* references.
*/
template <typename T>
std::tuple<const T&> toFlatAttributesTupleRef(const T& arg) {
return {arg};
}
template <typename... Ts>
auto toFlatAttributesTupleRef(const ComposedAttr<Ts...>& arg) {
return arg.attributes();
}
/**
* Same as above but does not pass by reference. Needs to be used when building composed hierarchies
* in helper functions
*/
template <typename T>
std::tuple<T> toFlatAttributesTuple(const T& arg) {
return {arg};
}
template <typename... Ts>
auto toFlatAttributesTuple(const ComposedAttr<Ts...>& arg) {
return arg.attributes();
}
template <typename... Ts>
auto ComposedAttr<Ts...>::attributes() const {
// logAttrs() converts the input to a loggable named attribute, user implementation
return std::apply(
[this](auto&&... args) { return std::tuple_cat(toFlatAttributesTuple(logAttrs(args))...); },
_values);
}
} // namespace detail
/**
* Combines multiple attributes to be returned in user defined logAttrs() functions
*/
template <typename... Ts>
auto multipleAttrs(Ts&&... attrs) {
// We can capture lvalue references as reference otherwise this is a temporary object that needs
// to be stored during the lifetime of the log statement.
return detail::ComposedAttr<
std::conditional_t<std::is_lvalue_reference_v<Ts>, Ts, std::remove_reference_t<Ts>>...>(
std::forward<Ts>(attrs)...);
}
} // namespace logv2
inline namespace literals {
inline fmt::internal::udl_arg<char> operator"" _attr(const char* s, std::size_t n) {
return fmt::operator""_a(s, n);
}
} // namespace literals
} // namespace mongo
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