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Newsgroups: comp.lang.ada
Date: Tue, 24 Sep 2019 15:09:35 -0700 (PDT)
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Subject: Re: Implementing Rust's borrow checked pointers
From: Lucretia <laguest9000@googlemail.com>
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Xref: reader01.eternal-september.org comp.lang.ada:57190
Date: 2019-09-24T15:09:35-07:00
List-Id: <comp.lang.ada>

On Tuesday, 24 September 2019 20:13:33 UTC+1, Keith Thompson  wrote:
> Lucretia <no> writes:
> > On Tuesday, 24 September 2019 12:23:30 UTC+1, Optikos  wrote:
> >
> >> > begin
> >> >    A.all ... ; -- raises exception.
> >> 
> >> No, to be as useful as Rust's borrow checker, instead of raising
> >> exception, it needs to be a compile-time error.  The compiler needs
> >> to maintain a whole-program directed graph at compile-time, not defer
> >> a detection-based localized analysis to run-time.
> >
> > Yes, the compiler would raise that exception at compile time. This
> > idea that all exceptions are raised at runtime is false and you should
> > check the AARM.
> 
> Can you provide a specific citation?

No, I'm fairly sure I saw it in one of the AARM's under compilation requirements years ago, but I cannot find it now.

> Certainly a compiler can diagnose an error at compile time, but I've
> never heard that referred to as an "exception".  And a compiler can
> generate code that unconditionally raises an exception, but that code is
> executed at run time.

I read it as the environment raises an exception like program_error on a compilation error.