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Subject: Re: Clause "with and use"
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Date: 2003-11-09T01:49:03-05:00
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Martin Dowie wrote:

>> A more interesting question is that
>>obviously if A in A := B * C; is indefinite, you want it to get the
>>"right" constraint from the "*" function.  But what if the return value
>>is declared indefinite?  Can it take its constraints from the target
> 
> object?
> 
> Sorry, it is v.late, I'm not sure what you mean here... Do you mean
> 'what if "B" and "C" are functions returning indefinite values?'

No, you have to think about this in the sequence I stated:

A: Matrix := B * C;
-- In this case A is not constrained and must get its constraint from
-- the function return value.  This is expected and should be allowed.

A: Matrix(1..4;1..4) := B * C;
-- Here we have a constrained object, now let's look inside the
-- function:

    function "*" (L,R: Matrix) return Matrix is
      Result: return Maxtrix := (others => others => 0.0);
      -- here we have a result--with whatever the declaration syntax is
      -- is this declaration--where the bounds come from the target.
      -- Should this be legal?

      -- In the non-limited case, the answer seems to be "What are you,
      -- nuts?  Of course you can't do that.  But where the type of the
      -- result is limited, the answer isn't so clear.  The result is
      -- going to have to be "built in place" in storage passed by the
      -- caller.  Being able to query the attributes of the result
      -- object is not so crazy in that case.  But do we want the rules
      -- to differ based on whether or not the object is limited?

      -- Remember the view of the type at the place of the call could be
      -- different from inside the function.

      -- My answer is that any rules are going to have to depend on the
      -- status of the type at the point of the function declaration.

      -- But that rule starts to produce other anomalies.  A rule that
      -- peeks inside the private part of a package with a function
      -- limited return type is possible.
    begin
      some code;
    end "*";

-- 
                                           Robert I. Eachus

100% Ada, no bugs--the only way to create software.