On Wed, Sep 20, 2000 at 03:25:11PM -0700, Steve Fink wrote:
> > > complains, but
> > >
> > > $x = 3; $x = 3
> >
> > As it shouldn't; you've mentioned $x twice, which means you probably didn't
> > misspell it. That your mentioning twice in this manner is silly is beyond
> > perl's grasp.
>
> Actually, it isn't. I've often written $x = $x = 3 simply to avoid this
> warning, because in the current implementation perl can't several of the
> different ways of using a variable.
Which is silly, because you shouldn't have to say '$x = $x = 3' when you
mean '$x = 3'. Just because there's a real reason behind it doesn't make it
any less silly.
> But I think you're missing the point. Why would you assign a value to a
> variable, but then never use that variable's value? All typos would be
> caught by the "initialized but never used" warning, as well as other
> mistakes.
So, in the code:
$foobal = 3;
if (@ARGV) {
$foobar = @ARGV;
}
print $foobar;
Only warn me that $foobar is uninitialized? I always prefer it when the
actual source of my problem is pointed out, rather than its symptoms.
> > Whoa, are you saying that saying 'my $x' no longer means $x has the value
> > undef? What value does it have? How can this be a good thing?
>
> No. No semantics change. This RFC is... what's the opposite of
> far-reaching? It changes no semantics. It only adds warnings. 'my $x'
> still means $x's value is undefined (but please do not say "the _value_
> undef").
I'm saying the value undef now, because that's exactly what it is, now. I
have learned that 'my $foo' is an implicit 'my $foo = undef', for all
intents and purposes.
> my $x;
> ...some code that might set $x to some value...
> if (defined ($x)) { ... }
>
> is bad, but
This is an idiom I use all the time, and I don't see anything wrong with it.
The value is undef, and I don't want to see this change at all.
> my $x = undef; # or my $x; undef $x;
I just have to say, ick. 'my $x' is easy, 'my $x = undef' is slightly
annoying. 'my $x; undef $x;' is confusing; declare a variable, and then
immediately undefine it, so I can avoid uninitialized value warnings?
Blech. What of a list of declarations, 'my($foo, $bar, $blah)'? do I get
lots of warnings unless I assign undef to, or undef, all of those?
> This is the same as in gcc; in gcc, the compiler remembers whether an
> integer variable has been initialized, and complains when you use it. But
> at runtime, that variable has some numeric value (a junk value, zero more
> often than not.)
I never particularly liked this feature of C, that a variable had junk in it
naturally until you assigned something to it. I much prefer how Perl does
it; give it a sane value, but warn whenever that value is used unless it was
intentional (by using defined or conditionals).
> Perl's runtime specifically tracks variables and expressions whose value
> is undefined, and does it well enough that most people think of 'undef' as
> being just another value.
It is just another value AFAIK, PL_sv_undef.
Michael
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