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Newsgroups: comp.lang.ada
Date: Sun, 17 Oct 2021 11:31:23 -0700 (PDT)
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Subject: Re: Is this legal?
From: Simon Belmont <sbelmont700@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:63027
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On Sunday, October 17, 2021 at 4:41:17 AM UTC-4, AdaMagica wrote:

> The accessibility rules are far too complicated and unreadable (I'm not a=
bout trying to grock them), but the component current has a type that has a=
 lifetime as long as Main. Your object o may be declared in an inner scope =
with less lifetime. Thus the assignment must be illegal.=20

I only ask because there are two rules, one that says the scope of the obje=
ct must be *statically* deeper than the return type of the function to be l=
egal, but then another similar one down the page that says a runtime check =
is made to ensure it (which begs the question of why the runtime check is n=
eeded if it must be done statically).  Normally things like that are for ed=
ge cases with anonymous access types, so it's not immediately obvious (to m=
e, at least) if GNAT is blowing the static check or the dynamic check (Or b=
oth?  Or neither?)

6.4.1~6.3/3
  In a function call, the accessibility level of the actual object for each=
 explicitly aliased parameter shall not be statically deeper than the acces=
sibility level of the master of the call (see 3.10.2).

6.4.1~15.1/3
In a function call, for each explicitly aliased parameter, a check is made =
that the accessibility level of the master of the actual object is not deep=
er than that of the master of the call (see 3.10.2).