Variable declaration

nagalenoj has asked for the wisdom of the Perl Monks concerning the following question:

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Re: Variable declaration by GrandFather (Saint) on Oct 14, 2011 at 06:33 UTC
$new::variable is a package variable belonging to the 'new' package (bad name btw). $another_variable is a lexical variable that you need to declare using 'my' because you are using strictures (`use strict; use warnings;` - highly recommended btw). The fix is just: `use strict; use warnings; use MyPackage; $MyPackage::variable = 1; my $another_variable = 2;` [download] Note that if package MyPackage uses strict it will need to declare $variable using our: `use MyPackage; use strict; use warnings; our $variable = 1;` [download] True laziness is hard work	[reply] [d/l] [select]
Re^2: Variable declaration by Eliya (Vicar) on Oct 14, 2011 at 07:14 UTC
$another_variable is a lexical variable... Strictly speaking, `$another_variable` (as the OP has it) isn't a lexical variable. `my` declares a lexical variable — no `my`, no lexical variable... (maybe you meant to say it should be a lexical variable?). In the OP's case, both variables are package variables, it's just that strictures do not complain if you use the fully-qualified form, even if the variable is otherwise undeclared (the idea being that you know what you're doing if you spell it this way).	[reply] [d/l] [select]
Re: Variable declaration by fisher (Priest) on Oct 14, 2011 at 06:10 UTC
You 'use strict' and do not declare the scope of your variable; just add before actual usage a declaration like this: `my $another_variable;` [download] And variable $new::variable already declared in package 'new'.	[reply] [d/l]
Re: Variable declaration by Anonymous Monk on Oct 14, 2011 at 06:11 UTC
read the documentation for strict, esp "strict vars", it explains the difference, between a fully qualified symbol ( one with ::) and an unqualified one :) Its also covered in http://learn.perl.org/books/beginning-perl/, Modern Perl: the free book , and Tutorials :)	[reply]
Re^2: Variable declaration by Anonymous Monk on Oct 14, 2011 at 06:13 UTC
A classic on the topic is Tutorials: Getting Deeper Into Perl: Coping with Scoping	[reply]
Re: Variable declaration by Ovid (Cardinal) on Oct 17, 2011 at 15:14 UTC
In addition to the other comments, I recommend new programmers also use diagnostics. Not only does that give you more information about the error, it also gives you suggestions on how to fix it. Here's the output I get when I include that: Global symbol "$another_variable" requires explicit package name at di +ag.pl line 6. Execution of diag.pl aborted due to compilation errors (#1) (F) You've said "use strict" or "use strict vars", which indicates + that all variables must either be lexically scoped (using "my" or +"state"), declared beforehand using "our", or explicitly qualified to say which package the global variable is in (using "::"). Uncaught exception from user code: Global symbol "$another_variable" requires explicit package na +me at diag.pl line 6. Execution of diag.pl aborted due to compilation errors. at diag.pl line 6 [download]	[reply] [d/l]