ANY NONE STREAM
deferred class interface FILTER_OUTPUT_STREAM
   --
   -- A filtered output stream.
   --

feature(s) from STREAM
   is_connected: BOOLEAN
      -- True if the filter is connected to some underlying stream.

   disconnect
      -- Disconnect from the underlying stream.
      require
         is_connected
      require else
         is_connected
      ensure
         not is_connected;
         stream = Void;
         filter = Void

   is_filtered: BOOLEAN

   detach
      ensure
         not is_filtered

feature(s) from OUTPUT_STREAM
   put_character (c: CHARACTER)
      require
         is_connected;
         not is_filtered and then can_put_character(c)

   flush
      -- Flushes the pipe. If is_filtered, calls the filter's
      -- flush instead.
      require
         is_connected

   can_put_character (c: CHARACTER): BOOLEAN

feature(s) from OUTPUT_STREAM
   put_string (s: STRING)
      -- Output s to current output device.
      require
         is_connected;
         not is_filtered;
         s /= Void

   put_unicode_string (unicode_string: UNICODE_STRING)
      -- Output the UTF-8 encoding of the unicode_string.
      require
         is_connected;
         not is_filtered;
         unicode_string /= Void

feature(s) from OUTPUT_STREAM
   -- To write a number:

   put_integer (i: INTEGER_64)
      -- Output i to current output device.
      require
         is_connected;
         not is_filtered

   put_integer_format (i: INTEGER_64; s: INTEGER)
      -- Output i to current output device using at most s character.
      require
         is_connected;
         not is_filtered

   put_real (r: REAL)
      -- Output r to current output device.
      require
         is_connected;
         not is_filtered

   put_real_format (r: REAL; f: INTEGER)
      -- Output r with only f digit for the fractionnal part.
      -- Examples:
      --    put_real(3.519,2) print "3.51".
      require
         is_connected;
         not is_filtered;
         f >= 0

   put_double (d: DOUBLE)
      -- Output d to current output device.
      require
         is_connected;
         not is_filtered

   put_double_format (d: DOUBLE; f: INTEGER)
      -- Output d with only f digit for the fractionnal part.
      -- Examples:
      --    put_double(3.519,2) print "3.51".
      require
         is_connected;
         not is_filtered;
         f >= 0

   put_number (number: NUMBER)
      -- Output the number.
      require
         is_connected;
         not is_filtered;
         number /= Void

feature(s) from OUTPUT_STREAM
   -- Other features:

   put_boolean (b: BOOLEAN)
      -- Output b to current output device according
      -- to the Eiffel format.
      require
         is_connected;
         not is_filtered

   put_pointer (p: POINTER)
      -- Output a viewable version of p.
      require
         is_connected;
         not is_filtered

   put_new_line
      -- Output a newline character.
      require
         is_connected;
         not is_filtered

   put_spaces (nb: INTEGER)
      -- Output nb spaces character.
      require
         is_connected;
         not is_filtered;
         nb >= 0

   append_file (file_name: STRING)
      require
         is_connected;
         not is_filtered;
         file_exists(file_name)

feature(s) from FILTER
   connect_to (a_stream: OUTPUT_STREAM)
      -- Connect the filter to some underlying stream.
      require
         not is_connected;
         a_stream.is_connected;
         not a_stream.is_filtered
      ensure
         is_connected

feature(s) from FILTER
   do_detach
      -- Used by the underlying stream to require not to be filtered anymore


invariant

    stream /= Void implies stream.filter = Current;

end of deferred FILTER_OUTPUT_STREAM