Class input_stream_adapter

Source/external/json.hpp:6153–6202

! 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. Clears the std::istream flags; any 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&&) = 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, e.g. 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 == std::char_traits<char>::eof()))
		{
			is->clear(is->rdstate() | std::ios::eofbit);
		}
		return res;
	}

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

// General-purpose iterator-based adapter. It might not be as fast as