common_containers.hpp

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#pragma once
 
/// @file userver/formats/parse/common_containers.hpp
/// @brief Parsers and converters for Standard Library containers and
/// std::optional
///
/// @ingroup userver_universal userver_formats_parse
 
#include <optional>
#include <string_view>
#include <type_traits>
 
#include <userver/formats/common/meta.hpp>
#include <userver/formats/parse/to.hpp>
#include <userver/utils/meta.hpp>
 
namespace boost::uuids {
struct uuid;
}
 
USERVER_NAMESPACE_BEGIN
 
namespace utils::impl::strong_typedef {
struct StrongTypedefTag;
}
 
namespace formats::parse {
 
namespace impl {
 
template <typename T, class Value>
inline T AsExtractor(const Value& value) {
    return value.template As<T>();
}
 
template <typename T, class Value>
inline T ConvertToExtractor(const Value& value) {
    return value.template ConvertTo<T>();
}
 
template <typename ArrayType, class Value, typename ExtractFunc>
ArrayType ParseArray(const Value& value, ExtractFunc extract_func) {
    value.CheckArrayOrNull();
    ArrayType response;
    auto inserter = std::inserter(response, response.end());
 
    for (const auto& subitem : value) {
        *inserter = extract_func(subitem);
        ++inserter;
    }
 
    return response;
}
 
template <typename ObjectType, class Value, typename ExtractFunc>
ObjectType ParseObject(const Value& value, ExtractFunc extract_func) {
    using KeyType = typename ObjectType::key_type;
 
    value.CheckObjectOrNull();
    ObjectType result;
 
    for (auto it = value.begin(); it != value.end(); ++it) {
        if constexpr (std::is_constructible_v<KeyType, std::string>) {
            result.emplace(it.GetName(), extract_func(*it));
        } else {
            result.emplace(Parse(std::string_view(it.GetName()), To<KeyType>{}), extract_func(*it));
        }
    }
 
    return result;
}
 
}  // namespace impl
 
template <typename T, typename Value>
std::enable_if_t<
    common::kIsFormatValue<Value> && meta::kIsRange<T> && !meta::kIsMap<T> && !std::is_same_v<T, boost::uuids::uuid> &&
        !std::is_convertible_v<T&, utils::impl::strong_typedef::StrongTypedefTag&>,
    T>
Parse(const Value& value, To<T>) {
    return impl::ParseArray<T>(value, &impl::AsExtractor<meta::RangeValueType<T>, Value>);
}
 
template <typename T, typename Value>
std::enable_if_t<common::kIsFormatValue<Value> && meta::kIsMap<T>, T> Parse(const Value& value, To<T>) {
    return impl::ParseObject<T>(value, &impl::AsExtractor<typename T::mapped_type, Value>);
}
 
template <typename T, typename Value>
std::optional<decltype(Parse(std::declval<Value>(), To<T>{}))> Parse(const Value& value, To<std::optional<T>>) {
    if (value.IsMissing() || value.IsNull()) {
        return std::nullopt;
    }
    return value.template As<T>();
}
 
template <class Value>
std::optional<std::nullptr_t> Parse(const Value&, To<std::optional<std::nullptr_t>>) {
    static_assert(!sizeof(Value), "optional<nullptr_t> is forbidden, check IsNull() instead");
    return nullptr;
}
 
template <typename T, typename Value>
std::enable_if_t<
    meta::kIsRange<T> && !meta::kIsMap<T> && !std::is_same_v<T, boost::uuids::uuid> &&
        !std::is_convertible_v<T&, utils::impl::strong_typedef::StrongTypedefTag&>,
    T>
Convert(const Value& value, To<T>) {
    if (value.IsMissing()) {
        return {};
    }
    return impl::ParseArray<T>(value, &impl::ConvertToExtractor<meta::RangeValueType<T>, Value>);
}
 
template <typename T, typename Value>
std::enable_if_t<meta::kIsMap<T>, T> Convert(const Value& value, To<T>) {
    if (value.IsMissing()) {
        return {};
    }
    return impl::ParseObject<T>(value, &impl::ConvertToExtractor<typename T::mapped_type, Value>);
}
 
template <typename T, typename Value>
std::optional<T> Convert(const Value& value, To<std::optional<T>>) {
    if (value.IsMissing() || value.IsNull()) {
        return std::nullopt;
    }
    return value.template ConvertTo<T>();
}
 
template <class Value>
std::optional<std::nullptr_t> Convert(const Value&, To<std::optional<std::nullptr_t>>) {
    static_assert(!sizeof(Value), "optional<nullptr_t> is forbidden, check IsNull() instead");
    return nullptr;
}
 
}  // namespace formats::parse
 
USERVER_NAMESPACE_END