Class ordered_map

3rd/nlohmann_json/include/nlohmann/ordered_map.hpp:21–188

template <class Key, class T, class IgnoredLess = std::less<Key>,
          class Allocator = std::allocator<std::pair<const Key, T>>>
                  struct ordered_map : std::vector<std::pair<const Key, T>, Allocator>
{
    using key_type = Key;
    using mapped_type = T;
    using Container = std::vector<std::pair<const Key, T>, Allocator>;
    using typename Container::iterator;
    using typename Container::const_iterator;
    using typename Container::size_type;
    using typename Container::value_type;

    // Explicit constructors instead of `using Container::Container`
    // otherwise older compilers choke on it (GCC <= 5.5, xcode <= 9.4)
    ordered_map(const Allocator& alloc = Allocator()) : Container{alloc} {}
    template <class It>
    ordered_map(It first, It last, const Allocator& alloc = Allocator())
        : Container{first, last, alloc} {}
    ordered_map(std::initializer_list<T> init, const Allocator& alloc = Allocator() )
        : Container{init, alloc} {}

    std::pair<iterator, bool> emplace(const key_type& key, T&& t)
    {
        for (auto it = this->begin(); it != this->end(); ++it)
        {
            if (it->first == key)
            {
                return {it, false};
            }
        }
        Container::emplace_back(key, t);
        return {--this->end(), true};
    }

    T& operator[](const Key& key)
    {
        return emplace(key, T{}).first->second;
    }

    const T& operator[](const Key& key) const
    {
        return at(key);
    }

    T& at(const Key& key)
    {
        for (auto it = this->begin(); it != this->end(); ++it)
        {
            if (it->first == key)
            {
                return it->second;
            }
        }

        JSON_THROW(std::out_of_range("key not found"));
    }

    const T& at(const Key& key) const
    {
        for (auto it = this->begin(); it != this->end(); ++it)