Re: declaration of variables

I think davido said it all in Re: declaration of variables, but he failed to comment on the last possibility that you mentioned.

m ($var) = "";
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I have no idea where you got that from. The simplest explanation would be that it is a typo and that you in fact meant:

my ($var) = "";
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If that is what you meant, read no further.

You're reading further. Ok, what you wrote almost has meaning. But should probably only be used in obfuscations, never in real code.

m ($var) = "";
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is basically equivalent with:

$_ =~ m/$var/ = "";
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which of course is an error, namely:

Can't modify pattern match (m//) in scalar assignment

But had your example shown just:

m ($var);
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that code would have compiled to:

$_ =~ m/$var/;
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if you don't use use strict; (which you don't in your example). A scary thought.

Therefore, once again, always use strict; (and use warnings; if you're using Perl 5.6.0 or later).

Liz

Update:
Made a little clearer with what I meant with "It".

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Re: Re: declaration of variables by tsee (Curate) on Sep 02, 2003 at 09:23 UTC
(Update: Sorry for the confusion. Until Liz' update about the fact that she was talking about "m ($v) =..." in the second half of her reply, I mistook her reply to be talking about the ordinary "my ($v) = 'a';".) Hi Liz, I don't think "my ($v) = '';" is equivalent to "$_ =~ m/$var/ = '';" and throwing a warning. `(cmd.exe has different shell quoting!) %perl -w -Mstrict -e "my ($v) = '';" (no warnings)` [download] And thus: `%perl -w -Mstrict -e "my ($v) = 'a'; print $v;" a` [download] which parses in my head as 'string is assigned to first element of the left hand side list'. I can't argue with the exact concepts applied by the interpreter because I forgot most about the weirder rules of context including lvalue stuff. But this seems to support the above: `%perl -w -Mstrict -e "my ($v,$s) = 'a'; print $v, $s;" aUse of uninitialized value in print at -e line 1.` [download] Still, string being assigned to first element of the left-hand side list. Same for lists on the right-hand side. (Which would be common usage in contrast to the above weirdness.) `%perl -w -Mstrict -e "my ($v,$s) = ('a'); print $v, $s;" aUse of uninitialized value in print at -e line 1.` [download] Good. As expected. Same goes for two-element lists on the rhs. `%perl -w -Mstrict -e "my ($v,$s) = ('a', 'b'); print $v, $s;" ab` [download] And the ',' operator has lower precedence than '=', so we get a 'useless use of a constant' error. `%perl -w -Mstrict -e "my ($v,$s) = 'a', 'b'; print $v, $s;" Useless use of a constant in void context at -e line 1. aUse of uninitialized value in print at -e line 1.` [download] Hope this clarified things a little.	[reply] [d/l] [select]

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Re: Re: declaration of variables
by tsee (Curate) on Sep 02, 2003 at 09:23 UTC

(cmd.exe has different shell quoting!)
%perl -w -Mstrict -e "my ($v) = '';"
(no warnings)
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%perl -w -Mstrict -e "my ($v) = 'a'; print $v;"
a
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%perl -w -Mstrict -e "my ($v,$s) = 'a'; print $v, $s;"
aUse of uninitialized value in print at -e line 1.
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%perl -w -Mstrict -e "my ($v,$s) = ('a'); print $v, $s;"
aUse of uninitialized value in print at -e line 1.
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%perl -w -Mstrict -e "my ($v,$s) = ('a', 'b'); print $v, $s;"
ab
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%perl -w -Mstrict -e "my ($v,$s) = 'a', 'b'; print $v, $s;"
Useless use of a constant in void context at -e line 1.
aUse of uninitialized value in print at -e line 1.
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