aggregates.hpp

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#pragma once
 
/// @file userver/dump/aggregates.hpp
/// @brief Dumping support for aggregates
///
/// @ingroup userver_dump_read_write
 
#include <type_traits>
 
#include <boost/pfr/core.hpp>
#include <boost/pfr/tuple_size.hpp>
 
#include <userver/dump/operations.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace dump {
 
template <typename T>
struct IsDumpedAggregate {};
 
namespace impl {
 
// Only the non-specialized IsDumpedAggregate struct is defined,
// the specializations are declared without a definition
template <typename T>
concept IsDumpedAggregateSpecialized = requires { sizeof(IsDumpedAggregate<T>); };
 
template <typename T, std::size_t... Indices>
constexpr bool AreAllDumpable(std::index_sequence<Indices...>) {
    return (kIsDumpable<boost::pfr::tuple_element_t<Indices, T>> && ...);
}
 
template <typename T>
constexpr bool IsDumpableAggregate() {
    if constexpr (std::is_aggregate_v<T> && !IsDumpedAggregateSpecialized<T>) {
        constexpr auto kSize = boost::pfr::tuple_size_v<T>;
        static_assert(
            AreAllDumpable<T>(std::make_index_sequence<kSize>{}),
            "One of the member of an aggregate that was marked as dumpable "
            "with dump::IsDumpedAggregate is not dumpable. Did you forget "
            "to include <userver/dump/common.hpp>, "
            "<userver/dump/common_containers.hpp> or some other header with "
            "Read and Write functions declarations?"
        );
        return true;
    } else {
        return false;
    }
}
 
template <typename T, std::size_t... Indices>
T ReadAggregate(Reader& reader, std::index_sequence<Indices...>) {
    // `Read`s are guaranteed to occur left-to-right in brace-init
    return T{reader.Read<boost::pfr::tuple_element_t<Indices, T>>()...};
}
 
}  // namespace impl
 
/// @brief Aggregates dumping support
///
/// To enable dumps and loads for an aggregate, add in the global namespace:
///
/// @snippet core/src/dump/aggregates_test.cpp  IsDumpedAggregate declaration
///
/// @warning Don't forget to increment format-version if data layout changes
template <typename T>
requires(impl::IsDumpableAggregate<T>())
void Write(Writer& writer, const T& value) {
    boost::pfr::for_each_field(value, [&writer](const auto& field) { writer.Write(field); });
}
 
/// @brief Aggregates deserialization from dump support
///
/// To enable dumps and loads for an aggregate, add in the global namespace:
///
/// @snippet core/src/dump/aggregates_test.cpp  IsDumpedAggregate declaration
///
/// @warning Don't forget to increment format-version if data layout changes
template <typename T>
requires(impl::IsDumpableAggregate<T>())
T Read(Reader& reader, To<T>) {
    constexpr auto kSize = boost::pfr::tuple_size_v<T>;
    return impl::ReadAggregate<T>(reader, std::make_index_sequence<kSize>{});
}
 
}  // namespace dump
 
USERVER_NAMESPACE_END