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Date: 17 Dec 92 14:29:35 GMT
From: aio!dnsurber@eos.arc.nasa.gov  (Douglas N. Surber)
Subject: Re: Novice Question on Record Representation
Message-ID: <dnsurber.724602575@node_26400>
List-Id: <comp.lang.ada>

In <1992Dec16.225712.23791@saifr00.cfsat.honeywell.com> lam@saifr00.cfsat.honey
well.com (Josh Lam) writes:

>There is a type in another package I need to use in a record in my package.
>Unfortunately, that type is private and I need to use record representation
>for my record.

> for My_Rec use record
>    A      at 0 range 0..15;
>    B      at 0 range 16..31;
>    C      at 1 range 0..31;     -- of course there is an error here!
>    Choice at 2 range 0..31;
>    D      at 0 range 0..15;
> end record;

Try the following small kludge:

    package P1 is
	type T is private;
	T_Size : constant := 32;
    private
	type T is new Integer;
	subtype Assertion is boolean range true .. true;
	a1 : constant Assertion := T_Size = T'Size;
    end P1;

    with P1;
    package P2 is
	type T is 
	    record
		F : P1.T;
	    end record;
	for T use record
	    F at 0 range 0 .. P1.T_Size - 1;
	end record;
    end P2;

You can't use P1.T'Size directly since it isn't static outside of the
private part (at least according to the Alsys compiler).  By using the
Assertion, you assure that T_Size has the right value.  Yes, you may have
to tweak its value when you port, but you can't get a clean compile with
the wrong value so it is safe.


--
Douglas Surber             "Would you rather debug at
Lockheed                    compile time or run time?"
Houston, TX                      --Michael B. Feldman