Re: [MacPerl] defining variables if not already defined

[Tom Sackett <tsackett@adobe.com>]

Paul-

Thanks for the info. I was aware that that, in effect, I was "my"ing a
variable twice in the same scope. However, what I don't understand is why
the second "my"ing was executed.

The sample code I provided was really just an illustration of the problem.
In the real-life code, that first line "my ($var) = "bongo";" sometimes
exists and sometimes doesn't. It's part of code that is generated on the
fly by another script. That's why I added the condition in line 3; I want
to define the "my" variable only if it is not already defined.

- Tom
 
At 07:45 PM 7/24/00 -0400, Paul Schinder wrote:
>At 4:14 PM -0700 7/24/00, Tom Sackett wrote:
>>I'm having a problem with the following code:
>>
>>    my ($var) = "bongo";
>>    print "The variable is: $var\n";
>>    my ($var) = "conga" unless (defined($var));
>>    print "The variable is now: $var\n";
>>
>>I would expect that this script would produce:
>>    The variable is: bongo
>>    The variable is now: bongo
>>
>>However, what I get is the following:
>>    The variable is: bongo
>>    The variable is now:
>>
>>The variable $var is losing its value, apparently because the first part of
>>line 3 is being partially executed (as if I had said "my ($var);" with no
>>assignment). I would expect that the first part of line 3 would not get
>>executed, because the condition (defined($var)) would evaluate as TRUE.
>>
>>The same thing happens no matter how I rewrite line 3, I've tried the
>>following:
>>   (my ($var) = "conga") unless (defined($var));
>>   my ($var) = "conga" if (!defined($var));
>>   (defined($var)) || (my ($var) = "conga");
>>
>>Any idea what's going on, or what I can do about it?
>
>It *did* give you an warning message, didn't it?
>
># "my" variable $var masks earlier declaration in same scope.
>File 'Untitled'; Line 3
>The variable is: bongo
>The variable is now:
>
>That's what's going on.  You're "my"ing a variable twice in the same 
>scope, which is A Bad Thing.
>
>Try
>
>    my $var = "bongo";
>    print "The variable is: $var\n";
>    $var = "conga" unless (defined($var));
>    print "The variable is now: $var\n";
>
>Or even better:
>
>#!perl -w
>use strict;
>    my $var = "bongo";
>    print "The variable is: $var\n";
>    $var= "conga" unless (defined($var));
>    print "The variable is now: $var\n";
>
>
>>
>>- Tom Sackett
>>   tsackett@iname.com
>>
>
>-- 
>--
>Paul Schinder
>schinder@pobox.com
>
>

# ===== Want to unsubscribe from this list?
# ===== Send mail with body "unsubscribe" to macperl-request@macperl.org