Re: "Common" data

[eachus@spectre.mitre.org (Robert I. Eachus)]

In article <CxLDB7.9DI@inmet.camb.inmet.com> stt@dsd.camb.inmet.com (Tucker Taft) writes:

  > I believe Robert Eachus misinterpreted this question.  I think the
  > question is very simple and very fundamental -- if two
  > different compilation units "with" the same package, do you
  > end up with just one copy of the data of the package, or
  > might you get one for each "with"?

  I won't argue about what the original question "meant."  If the
questioner is satisfied, fine.  Otherwise, we can try to refine the
question.  I assumed from the mention of comm code, that the question
had to do with keeping copies of variables in registers.

  > The answer is most definitely that you get exactly one
  > copy of the data of the package, no matter how many
  > times it is "with"ed.  This is so fundamental to Ada
  > that it may be hard to point to one single place in the manual
  > that says it straight out.  The introduction to chapter 10 comes 
  > closest to saying that a program has at most one copy of any given
  > compilation unit.  Also, when "with" clauses are explained,
  > they simply talk about making the "with"ed unit "visible."  

   If this is the issue, then the answer can be deduced by looking at
the elaboration rules.  For instance, for a variable declared in a
package specification withed by several units, look at 10.5(1),
7.2(3), and finally 3.2.1(7): "The object is created."
--

					Robert I. Eachus

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