Re^5: Help! My variables are jumping off a cliff!

I have also shown that it can be, and usually is, an error

You haven't. Your OP shows some code, but it's not clear to me whether there's an error. But even I grant you that you have shown that it's possible to make an error, you have utterly failed to even remotely convince me of the "usual" part.

To go back to your original code:

my $x = 1;          # Variable declaration
my $x = 10;         # Variable suicide!
print $x;
[download]

What's the error here? This prints 10. Should this have printed 1? Do note that if you'd had written:

my $x = 1;
$x = 10;
print $x;
[download]

it would have still printed 10.

You know, it happens probably a few times a week that my code triggers the "masks declaration" warning. I cannot recall a single time where this was actually causing a problem. Just removing the "my" fixes the problem; or a no warnings 'misc';.

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Re^6: Help! My variables are jumping off a cliff! by oko1 (Deacon) on Feb 27, 2012 at 00:50 UTC
I have indeed shown that it is an error - in the post preceding the one where I made that statement. To recap: you declare a variable in one part of a large program. Later, when adding code, you unintentionally declare the same variable again in another part of the program. You've just smashed the first one, and caused errors in any code that depended on it. The error is not that $x now contains 10. The error is that this can happen at all, with minimal (if any, depending on externals) warnings. -- I hate storms, but calms undermine my spirits. -- Bernard Moitessier, "The Long Way"	[reply]
Re^7: Help! My variables are jumping off a cliff! by Your Mother (Archbishop) on Feb 27, 2012 at 01:22 UTC
You should be using warnings and you can easily promote them to errors with `FATAL` or use something like strictures if its flavor is appealing. This bug has a strong code smell to it. If your code blocks/scopes are large enough that this is happening, they are too large. So I say. moo@cow[26]~>perl -Mstrict -le 'my $w = 1; my $w; print "OHAI"' OHAI moo@cow[27]~>perl -Mstrict -wle 'my $w = 1; my $w; print "OHAI"' "my" variable $w masks earlier declaration in same scope at -e line 1. OHAI moo@cow[28]~>perl -Mstrictures -le 'my $w = 1; my $w; print "OHAI"' "my" variable $w masks earlier declaration in same scope at -e line 1. moo@cow[29]~>perl -Mstrict -Mwarnings=FATAL,misc -le 'my $w = 1; my $w +; print "OHAI"' "my" variable $w masks earlier declaration in same scope at -e line 1. [download]	[reply] [d/l] [select]
Re^7: Help! My variables are jumping off a cliff! by JavaFan (Canon) on Feb 27, 2012 at 08:45 UTC
you declare a variable in one part of a large program. Later, when adding code, you unintentionally declare the same variable again in another part of the program. You've just smashed the first one, and caused errors in any code that depended on it. Unfortunally, it's impossible to determine whether any further uses of said variable depend on the original one (then there's an error), or on the new one (then using the same name is harmless). That's why Perl gives you a warning. A warning after all means "heh, coder, I spotted something that may be an error. But I can't know for sure, I'm just carrying on, cause, you know, I'm often quite mistaken about this". Just because you made a boo-boo in your code, that you didn't spot because you weren't running with warnings doesn't mean you now have a reason to claim "use strict" is broken. It's not. Your code was.	[reply]