Reprise: 'in out' parameters for functions

[Stephen Leake <stephen_leake@acm.org>]

I just ran across a need for an 'in out' parameter in a function, in
"real code", so I thought I post it here "just for fun" :).

This is what I wanted to declare:

function Parse
  (Error_Label : in     String;
   Token       : in out Token_List.List_Iterator)
  return String;
  --  Process Token, which should contain '([Config_File =>] <string>)'.
  --  Return the string.
  --  Delete parsed tokens from Token.

Token must be 'in out', because the next parse function called wants
to work on the stuff after the config file.

Parse must be a function, because I'm returning a String.

The work-around is to use a procedure and a bounded string:

   procedure Parse
     (Error_Label      : in     String;
      Token            : in out Token_List.List_Iterator;
      Config_File_Name :    out OpenToken.Buffers.Bounded_String);

In this instance, the body of Parse deals with
OpenToken.Buffers.Bounded_String anyway, so there's no actual new
overhead introduced. But the user interface is not as clean as it
could be.

-- 
-- Stephe