Re: [MacPerl] defining variables if not already defined

[Paul Schinder <schinder@pobox.com>]

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

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