Re: Protected Types and Address Clauses

[kst@thomsoft.com (Keith Thompson)]

In <4gcppr$10f5@watnews1.watson.ibm.com> ncohen@watson.ibm.com (Norman H. Cohen) writes:
> In article <4fqe6h$t0e@theopolis.orl.mmc.com>
> rgilbert@unconfigured.xvnews.domain (Bob Gilbert) wrote: 
> BG>  protected Discretes is
> BG>    procedure Write(Settings : in SETTING_LIST);
> BG>  private
> BG>    HW_Control : DISCRETE_HW_CONTROL;
> BG>    for HW_Control use at 16#4000_0001#;
> BG>  end Discretes;
[...]
> This just establishes that the syntax allows representation clauses in
> the private part of a protected definition.  I agree with Robert's
> conclusion that the RM appears (despite the intent of its authors) to
> permit this address clause, but as the result of a more intricate
> exegesis.  By J.7(2),
> 
>    for HW_Control use at 16#4000_0001#;
> 
> is equivalent to
> 
>    for HW_Control'Address use 16#4000_0001#;
> 
> 13.3(10) says that this attribute is defined if HW_Control denotes an
> object, program unit, or label.  In fact, HW_Control does denote an
> object, because 3.3(12) states that a component of an object is an
> object.
[...]

Yes, the 'Address attribute is defined for HW_Control; in fact you can
refer to HW_Control'Address from within the body of Discretes.Write.
That doesn't mean an address *clause* for HW_Control is legal.
RM95-13.3(12) says that

    Address may be specified for stand-alone objects and for program
    units via an attribute_definition_clause.

Since HW_Control is not a stand-alone object, an address clause for it
is not legal, any more than an address clause is legal for a label or
an array element.

(Incidentally, RM95-13.7(37) that System.Address should be private;
for implementations that follow this advice, 16#4000_0001# is not a
legal address.)

-- 
Keith Thompson (The_Other_Keith) kst@thomsoft.com
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