Re: Novice Question on Record Representation

[telesoft!garym@uunet.uu.net (Gary Morris @pulsar)]

In <dnsurber.724602575@node_26400> dnsurber@lescsse.jsc.nasa.gov (Douglas N. Su
rber) writes:
>    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;

>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. 

Unfortunately, you can't rely on assertion like this.  The constant a1 is
not used anywhere and an optimizing compiler could remove a1 and the
expression used for its initial value (TSize = T'Size).  So the range check
never occurs and no exception or compile time warning is generated.  This
optimization is allowed by 11.6(7), when the only effect of a predefined
operation is to raise an exception. 

--GaryM
-- 
Gary Morris                      Internet: garym@telesoft.com
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