Class lexer

3rd/nlohmann_json/single_include/nlohmann/json.hpp:6731–7930

*/
template<typename BasicJsonType, typename InputAdapterType>
class lexer : public lexer_base<BasicJsonType>
{
    using number_integer_t = typename BasicJsonType::number_integer_t;
    using number_unsigned_t = typename BasicJsonType::number_unsigned_t;
    using number_float_t = typename BasicJsonType::number_float_t;
    using string_t = typename BasicJsonType::string_t;
    using char_type = typename InputAdapterType::char_type;
    using char_int_type = typename std::char_traits<char_type>::int_type;

  public:
    using token_type = typename lexer_base<BasicJsonType>::token_type;

    explicit lexer(InputAdapterType&& adapter, bool ignore_comments_ = false) noexcept
        : ia(std::move(adapter))
        , ignore_comments(ignore_comments_)
        , decimal_point_char(static_cast<char_int_type>(get_decimal_point()))
    {}

    // delete because of pointer members
    lexer(const lexer&) = delete;
    lexer(lexer&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    lexer& operator=(lexer&) = delete;
    lexer& operator=(lexer&&) = default; // NOLINT(hicpp-noexcept-move,performance-noexcept-move-constructor)
    ~lexer() = default;

  private:
    /////////////////////
    // locales
    /////////////////////

    /// return the locale-dependent decimal point
    JSON_HEDLEY_PURE
    static char get_decimal_point() noexcept
    {
        const auto* loc = localeconv();
        JSON_ASSERT(loc != nullptr);
        return (loc->decimal_point == nullptr) ? '.' : *(loc->decimal_point);
    }

    /////////////////////
    // scan functions
    /////////////////////

    /*!
    @brief get codepoint from 4 hex characters following `\u`

    For input "\u c1 c2 c3 c4" the codepoint is:
      (c1 * 0x1000) + (c2 * 0x0100) + (c3 * 0x0010) + c4
    = (c1 << 12) + (c2 << 8) + (c3 << 4) + (c4 << 0)

    Furthermore, the possible characters '0'..'9', 'A'..'F', and 'a'..'f'
    must be converted to the integers 0x0..0x9, 0xA..0xF, 0xA..0xF, resp. The
    conversion is done by subtracting the offset (0x30, 0x37, and 0x57)
    between the ASCII value of the character and the desired integer value.

    @return codepoint (0x0000..0xFFFF) or -1 in case of an error (e.g. EOF or
            non-hex character)
    */