Class input_stream_adapter

Source/Utils/json.hpp:4790–4838

! Input adapter for a (caching) istream. Ignores a UFT Byte Order Mark at beginning of input. Does not support changing the underlying std::streambuf in mid-input. Maintains underlying std::istream and std::streambuf to support subsequent use of standard std::istream operations to process any input characters following those used in parsing the JSON input.

        subsequent call for input from the std::istream.
        */
        class input_stream_adapter
        {
        public:
            using char_type = char;

            ~input_stream_adapter()
            {
                // clear stream flags; we use underlying streambuf I/O, do not
                // maintain ifstream flags, except eof
                if (is != nullptr)
                {
                    is->clear(is->rdstate() & std::ios::eofbit);
                }
            }

            explicit input_stream_adapter(std::istream& i)
                : is(&i), sb(i.rdbuf())
            {}

            // delete because of pointer members
            input_stream_adapter(const input_stream_adapter&) = delete;
            input_stream_adapter& operator=(input_stream_adapter&) = delete;
            input_stream_adapter& operator=(input_stream_adapter&& rhs) = delete;

            input_stream_adapter(input_stream_adapter&& rhs) noexcept : is(rhs.is), sb(rhs.sb)
            {
                rhs.is = nullptr;
                rhs.sb = nullptr;
            }

            // std::istream/std::streambuf use std::char_traits<char>::to_int_type, to
            // ensure that std::char_traits<char>::eof() and the character 0xFF do not
            // end up as the same value, eg. 0xFFFFFFFF.
            std::char_traits<char>::int_type get_character()
            {
                auto res = sb->sbumpc();
                // set eof manually, as we don't use the istream interface.
                if (JSON_HEDLEY_UNLIKELY(res == EOF))
                {
                    is->clear(is->rdstate() | std::ios::eofbit);
                }
                return res;
            }

        private:
            /// the associated input stream
            std::istream* is = nullptr;
            std::streambuf* sb = nullptr;
        };

        // General-purpose iterator-based adapter. It might not be as fast as
        // theoretically possible for some containers, but it is extremely versatile.