variant.hpp

#pragma once
 
#include <variant>
 
#include <userver/formats/json/value.hpp>
#include <userver/formats/parse/to.hpp>
#include <userver/formats/serialize/to.hpp>
#include <userver/utils/meta.hpp>
#include <userver/utils/overloaded.hpp>
 
USERVER_NAMESPACE_BEGIN
 
namespace chaotic {
 
template <typename... T>
auto& GetVariant(std::variant<T...>& arg) {
    return arg;
}
 
template <typename... T>
const auto& GetVariant(const std::variant<T...>& arg) {
    return arg;
}
 
template <typename T>
decltype(T().AsVariant()) GetVariant(T& arg) {
    return arg.AsVariant();
}
 
template <typename... T>
struct Variant final {
    const std::variant<decltype(Parse(std::declval<formats::json::Value>(), formats::parse::To<T>{}))...>& value;
};
 
template <typename Value, typename... T>
auto Parse(const Value& value, formats::parse::To<Variant<T...>>) {
    return value.template As<std::variant<T...>>();
}
 
template <typename Value, typename... T>
Value Serialize(const Variant<T...>& var, formats::serialize::To<Value>) {
    return std::visit(
        utils::Overloaded{[](const formats::common::ParseType<Value, T>& item) {
            return typename Value::Builder(T{item}).ExtractValue();
        }...},
        var.value
    );
}
 
}  // namespace chaotic
 
USERVER_NAMESPACE_END