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From: tmoran@acm.org
Newsgroups: comp.lang.ada
Subject: Re: 'withing' problem
References: <3be907bc$0$233$ed9e5944@reading.news.pipex.net>
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Date: Wed, 07 Nov 2001 18:59:38 GMT
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Date: 2001-11-07T18:59:38+00:00
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> The implementation of 'print' would call 'toString(x)' and output the result.
  I thought toString might be intended for that, but then I'd expect it to
return a fixed type like String, not some extendable (ie, variable) type "seq".

> Correct. But the declaration of 'toString' needs to be in the package for
> 'anything', so the package for 'anything' needs to 'with' the package for
> 'seq', and vice versa.
> >   function toString(x:anything'class) return seq;

  If toString takes "anything'class", then it's not a primitive of "anything"
and needn't be declared in the same package as "anything".  In particular,
"toString" and "seq" can be declared together in a package that with's
the package that declares "anything".

package Root_Of_All is
  type anything is tagged null record;
  ...
end Root_Of_All;

with Root_Of_All;
package Debugging_Help is
  type seq is new anything with record
    ...
  end record;
  function toString(x:Root_Of_All.anything'class) return seq;
  -- yields "unprintable object" as seq
  -- Should be overloaded for printable objects
  ...
end Debugging_Help;

with Root_Of_All, Debugging_Help;
package Something is
  type heir is new ... --- descendent of "anything"
  function toString(x:heir'class) return seq;
  -- seq is suitable for printing for debugging or whatever
  ...