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Date: Wed, 6 May 2020 11:28:00 -0700 (PDT)
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Subject: Re: How can one record component be local and another not?
From: Jere <jhb.chat@gmail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:58615
Date: 2020-05-06T11:28:00-07:00
List-Id: <comp.lang.ada>

On Wednesday, May 6, 2020 at 1:30:58 PM UTC-4, Niklas Holsti wrote:
> On 2020-05-05 20:32, hreba wrote:
> > Ok, with all your hints I came to the following solution:
> >=20
> > --=20
> > package Aux is
> >  =C2=A0=C2=A0 type Integer_P is access all Integer;
> >  =C2=A0=C2=A0 type Rec is limited record
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 a: aliased Integer;
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 p: Integer_P;
> >  =C2=A0=C2=A0 end record;
> >=20
> >  =C2=A0=C2=A0 procedure Init (r: access Rec);
> > end Aux;
> > --=20
> > package body Aux is
> >  =C2=A0=C2=A0 procedure Init (r: access Rec) is
> >  =C2=A0=C2=A0 begin
> >  =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 r.p:=3D r.a'Access;
> >  =C2=A0=C2=A0 end Init;
> > end Aux;
> > --=20
> > with Aux;
> > procedure Test is
> >  =C2=A0=C2=A0 r:=C2=A0=C2=A0=C2=A0 aliased Aux.Rec;
> > begin
> >  =C2=A0=C2=A0 Aux.Init (r'Access);
> > end Test;
> > --=20
> >=20
> <SNIPPED>
> Somewhat surprisingly to me, any call of the form
> "Aux.Init (r'Unchecked_Access)" also works, whether "r" is a=20
> library-level object or a local (limited-life) object, even if=20
> "Aux.Init" itself uses "'Access" and not "'Unchecked_Access". Apparently=
=20
> the accessibility level provided in the value of Unchecked_Access is=20
> such as to make the check succeed, as for a library-level object.
>=20
Yeah, RM section 13.10 says it treats it as if the object were declared
at library level for Unchecked_Access

> I also found that a call like "Aux.Init (new Aux.Rec)", which applies=20
> "Aux.Init" to a heap-allocated "Rec" object, fails the accessibility=20
> check, so this check is really strict. Of course, the heap object can be=
=20
> deallocated at any time, so it may have a short life-time, but that can=
=20
> be done (mainly) by Unchecked_Deallocation, so it involves "unchecked"=20
> programming. Hm.
>=20
Is that because the heap allocated object is allocated using an
anonymous access type instead of a named access type per chance?
I know anonymous access types have different accessibility level
rules.  It might be setting the accessibility level to the point
of call maybe?