Re: Undefined behaviour [was Re: The D Programming Language]
"James Kanze" <james.kanze@gmail.com> writes:
Ian McCulloch wrote:
David Abrahams wrote:
There's no reason in principle that a C++ system couldn't be
written that immediately detects way, _way_ more of the errors
that lead to undefined behavior and invokes a debugger
immediately. Every pointer dereference could be fully checked,
for example.
Right - and there are systems that already do this. Valgrind (
http://www.valgrind.org/) springs to mind at this point. In the face of a
programming error, you want as much `undefined' behaviour as possible, to
give the tools that detect such behaviour the most information possible.
Except that you only need such tools because of the undefined
behavior.
Completely backwards. You can only _use_ such tools because of the
undefined behavior. You still need something to detect the incorrect
logic that in C++ would have caused UB and in Java causes
who-knows-what "defined" behavior. But no such tool exists, or can
exist.
Limit the cases of undefined behavior to the few that show up in
Java, and you don't need valgrind. Or rather, it doesn't help you,
That's more on target. It can't help you.
because it doesn't detect race conditions, etc., either. (At least,
I don't think it does.)
I think valgrind is the single most useful debugging tool on Linux, even
though I don't use it that often, much less frequently than a debugger, or
even printf() debugging[*]. AFAIU valgrind would be completely useless for
debugging java programs,
Because most of the types of errors it finds aren't possible in
Java. (The last error I found with valgrind was someone
deleting a local variable, for example. Impossible in Java.)
Right. The question is, does the elimination of UB (which, remember,
is a *response* to programming errors, not a cause) actually in and of
itself make it harder to make programming errors? I don't see how it
could.
Now, we can ask whether the design of Java in general makes it harder
to make programming errors. It may do that, I don't know. But it's
not because the language spec says there's no UB. AFAICT, the only
thing that the presence of UB can possibly affect is debuggability,
and as I've posted elsewhere, I doubt the effect is entirely negative.
--
Dave Abrahams
Boost Consulting
www.boost-consulting.com
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