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From: Simon Wright <simon@pogner.demon.co.uk>
Subject: Re: How do I get this to work??
Date: 1999/01/08
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Date: 1999-01-08T00:00:00+00:00
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Stephen Leake <Stephen.Leake@gsfc.nasa.gov> writes:

> I agree with the other comments here; the bad taste is from not
> knowing what will happen to the pointer when you pass it to C. That's
> why it is "unchecked".

Not just to C! for example, in the Booch Components, I have

  procedure Create_Arc (G : in out Undirected_Graph;
                        A : in out Undirected_Arc'Class;
                        I : Arc_Item;
                        First : in out Undirected_Vertex'Class;
                        Second : in out Undirected_Vertex'Class) is
  begin
    Clear (A);
    A.Rep := new Arc_Node'(Ada.Finalization.Controlled with
                           Item => I,
                           Enclosing => G'Unchecked_Access, -- <<<<<<<<<<<<<<<<
                           From => First.Rep,
                           To => Second.Rep,
                           Next_Incoming => null,
                           Next_Outgoing => null,
                           Count => 1);

and the Unchecked_Access is needed because (I suppose) you can't tell
at compile time what the scope of the actual for G is. It would
certainly be possible (though unnatural) to use this code with the
scope of the actual G being less than that of the actual A .. hmm, I
guess there's a warning-to-users needed there ..