Re: Subverting 'Access for Sub-programs

[adam@irvine.com]

In article <7oc5ih$6mb$1@wanadoo.fr>,
  "Jean-Pierre Rosen" <rosen.adalog@wanadoo.fr> wrote:
>
> OK, I understand your problem better (full examples always help :-)
> Of course, you realize that "Integrator" could store the pointer to
> function to any global variable, possibly resulting later in random
> branches. I think the trade-off in language design was that accessing
> random memory location was bad, but not THAT bad. OTOH, branching to
> random locations was considered really too dangerous. Even if you
> promise not to store the pointer to function to anything global, it
> would be a property of the body, i.e. something that could be changed
> without anybody noticing . . .

Couldn't it be made a property of the access type, instead of a
property of the body?

Was any solution like this considered, when Ada 95 was designed?  The
inability to take an 'ACCESS of an inner subprogram seems like an
obnoxious restriction, a step down from Pascal and Algol, and it seems
like programmers should have an option to remove this restriction at
the expense of adding restrictions elsewhere or perhaps adding runtime
checks.  In fact, I kind of like the idea of allowing a different kind
of subprogram access type declaration such that 3.10.2(28) wouldn't
apply to that type, where the program must check to make sure the
subprogram's ancestors are still on the stack when objects of the type
get dereferenced.  I suspect that in the Integrate case, the compiler
would even be able to tell that this runtime check is unnecessary.

Comments?
                                -- Adam


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