Function push_back

3rd/nlohmann_json/include/nlohmann/json.hpp:5451–5472

! @brief add an object to an array Appends the given element @a val to the end of the JSON value. If the function is called on a JSON null value, an empty array is created before appending @a val. @param[in] val the value to add to the JSON array @throw type_error.308 when called on a type other than JSON array or null; example: `"cannot use push_back() with number"`

    @since version 1.0.0
    */
    void push_back(basic_json&& val)
    {
        // push_back only works for null objects or arrays
        if (JSON_HEDLEY_UNLIKELY(!(is_null() || is_array())))
        {
            JSON_THROW(type_error::create(308, "cannot use push_back() with " + std::string(type_name()), *this));
        }

        // transform null object into an array
        if (is_null())
        {
            m_type = value_t::array;
            m_value = value_t::array;
            assert_invariant();
        }

        // add element to array (move semantics)
        const auto old_capacity = m_value.array->capacity();
        m_value.array->push_back(std::move(val));
        set_parent(m_value.array->back(), old_capacity);
        // if val is moved from, basic_json move constructor marks it null so we do not call the destructor
    }

    /*!
    @brief add an object to an array