optionals.hpp

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#pragma once
 
/// @file userver/utils/optionals.hpp
/// @brief Helper functions for std optionals
/// @ingroup userver_universal
 
#include <optional>
#include <string>
#include <utility>
 
#include <fmt/compile.h>
#include <fmt/format.h>
 
USERVER_NAMESPACE_BEGIN
 
namespace utils {
 
/// Converts std::optional to a string, empty value represented as "--"
template <class T>
std::string ToString(const std::optional<T>& from) {
    return from ? fmt::format(FMT_COMPILE(" {}"), *from) : "--";
}
std::string ToString(const std::optional<T>& from) {…}
 
/// A polyfill for C++23 monadic operations for `std::optional`.
template <typename T, typename Func>
auto OptionalTransform(T&& opt, Func func) -> std::optional<decltype(std::move(func)(*std::forward<T>(opt)))> {
    if (opt) return std::move(func)(*std::forward<T>(opt));
    return std::nullopt;
}
auto OptionalTransform(T&& opt, Func func) -> std::optional<decltype(std::move(func)(*std::forward<T>(opt)))> {…}
 
}  // namespace utils
 
USERVER_NAMESPACE_END