Re: Implementing Rust's borrow checked pointers

[Optikos <optikos@verizon.net>]

On Tuesday, September 24, 2019 at 3:31:15 PM UTC-5, Keith Thompson wrote:
> Optikos writes:
> > On Tuesday, September 24, 2019 at 2:13:33 PM UTC-5, Keith Thompson wrote:
> >> Lucretia <laguest9000@googlemail.com> writes:
> [...]
> >> > 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?
> >> 
> >> 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've seen compile-time exceptions, but they were compiler bugs, not
> >> diagnostics for the program being compiled.)
> >
> > Keith, I already did in a prior posting above, but you apparently
> > blocked me, so your loss.
> 
> I have not blocked you.  It's entirely possible that I missed your
> earlier article (I don't follow this newsgroup all that closely),
> or that I read it but didn't think it supported the assertion.
> 
> >                            Here is the answer to your question again
> > for all other readers: §1.1.5 Classification of •Errors “If such an
> > •error• situation is certain to arise in every execution of a
> > construct, then an implementation is •••allowed (although not
> > required)••• to report this fact at •compilation• time.”
> 
> That doesn't describe raising an exception at compilation time.
> It describes (optionally) *reporting* at compilation time that an
> exception is certain to be raised at run time.
> 
> Again, the claim (from Lucretia, not from you) was:
> 
>     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.

I already answered that in my 9:08AM reply today.  I demonstrated via extensive quotation from AARM that Luke utilized the incorrect term-of-art.  According to the AARM as written, Luke meant “error” (as quoted from AARM) when he wrote “exception” (as quoted from c.l.a).  With a relatively minor change from Luke's “raise exception” to emit error message at compile-time, Luke's statement is otherwise correct.

> Printing a warning message is not raising an exception.