json_ref.hpp

#pragma once
 
#include <initializer_list>
#include <utility>
 
#include <nlohmann/detail/meta/type_traits.hpp>
 
namespace nlohmann
{
namespace detail
{
template<typename BasicJsonType>
class json_ref
{
  public:
    using value_type = BasicJsonType;
 
    json_ref(value_type&& value)
        : owned_value(std::move(value))
    {}
 
    json_ref(const value_type& value)
        : value_ref(&value)
    {}
 
    json_ref(std::initializer_list<json_ref> init)
        : owned_value(init)
    {}
 
    template <
        class... Args,
        enable_if_t<std::is_constructible<value_type, Args...>::value, int> = 0 >
    json_ref(Args && ... args)
        : owned_value(std::forward<Args>(args)...)
    {}
 
    // class should be movable only
    json_ref(json_ref&&) noexcept = default;
    json_ref(const json_ref&) = delete;
    json_ref& operator=(const json_ref&) = delete;
    json_ref& operator=(json_ref&&) = delete;
    ~json_ref() = default;
 
    value_type moved_or_copied() const
    {
        if (value_ref == nullptr)
        {
            return std::move(owned_value);
        }
        return *value_ref;
    }
 
    value_type const& operator*() const
    {
        return value_ref ? *value_ref : owned_value;
    }
 
    value_type const* operator->() const
    {
        return &** this;
    }
 
  private:
    mutable value_type owned_value = nullptr;
    value_type const* value_ref = nullptr;
};
}  // namespace detail
}  // namespace nlohmann