More Scope related questions.

[curiousmonk]

In the examples below, the variable the declaration of $b without my, local or our works like a global variable. I know this issue will be solved if strictures and warnings are enabled(One would be forced to declare a scope specifier) but without that, the expected behaviour should be that unless you explicitly declare it as 'our' the scope of the variable should end immediately after the curly brace

Shouldn't the default scope be local?

case 1:

$ perl -e 'use Data::Dumper;{my @a=(0..10);$b=\@a} print Dumper $b'
$VAR1 = [
          0,
          1,
          2,
          3,
          4,
          5,
          6,
          7,
          8,
          9,
          10
        ];

case 2:

$ perl -e 'use Data::Dumper;{my @a=(0..10);my $b=\@a} print Dumper $b'
$VAR1 = undef;

case 3:

$ perl -e 'use Data::Dumper;{my @a=(0..10);local $b=\@a} print Dumper 
+$b'
$VAR1 = undef;

case 4:

$ perl -e 'use Data::Dumper;{my @a=(0..10);our $b=\@a} print Dumper $b
+'
$VAR1 = [
          0,
          1,
          2,
          3,
          4,
          5,
          6,
          7,
          8,
          9,
          10
        ];

[BrowserUk]

Shouldn't the default scope be local?

Should or should not doesn't enter into it. It isn't.

For why, read 25 years of history.

[LanX]

> Shouldn't the default scope be local?

No, the default isn't scoped at all¹ and the variables are globally accessible package vars.

our is similar, but the (compile time) declaration is scoped.

our was introduced comparatively late. Before that you needed to use vars to be strict.

Try searching the archives, it's full of explanations and comparative examples.

¹) some languages do, but Perl follows the mainstream tradition.

[kcott]

G'day curiousmonk,

Your question appears to have been answered in the responses you've already received. I might just point out that $a and $b were poor choices for your examples as they're special variables that don't require declaration. Here's an excerpt from perlvar:

• $a
• $b
  Special package variables ... Because of this specialness $a and $b don't need to be declared (using use vars, or our()) even when using the strict 'vars' pragma. ...

[curiousmonk]

Thanks, this was one thing I didn't know about. It just all boils down to reading documentation properly

Just as you said

$ perl -e 'use strict;use Data::Dumper;{my @c=(0..10);$d=\@c} print Du
+mper $d'
Global symbol "$d" requires explicit package name at -e line 1.
Global symbol "$d" requires explicit package name at -e line 1.

Doesn't work, but

$ perl -e 'use strict;use Data::Dumper;{my @a=(0..10);$b=\@a} print Du
+mper $b'
$VAR1 = [
          0,
          1,
          2,
          3,
          4,
          5,
          6,
          7,
          8,
          9,
          10
        ];

Does

[2teez]

Hi curiousmonk,
Please, you need read these:

• Temporary Values via local()
• Private Variables via my()

The Perl documentation perlsub tell the story...

[Anonymous Monk]

but without that, the expected behaviour

:) First you learn the rules, then you can have expectations realistic expectations

If you're expecting a different behaviour, you're expecting according to another set of rules, not perl's set of rules :)

Tutorials: Variable Scoping in Perl: the basics, Coping with Scoping , Mini-Tutorial: Perl's Memory Management, Lexical scoping like a fox, Read this if you want to cut your development time in half!, Closure on Closures