Here's another example just to show the difference between scopes: 
#!/usr/bin/perl -w
use strict;

package R;
my $R = 10;
use vars qw( $var );
$var = 20;

package main;
print "R is >>$R<<\n";

package R;
print "R is >>$R<<\n";
print "var is >>$var<<\n";

[download]
Nifty, everything prints. All in the same file, everything okay, right? Let's mess with scoping a little bit: 
#!/usr/bin/perl -w
use strict;

{
package R;
my $R = 10;
use vars qw( $var );
$var = 20;
}

package main;
print "R is >>$R<<\n";
print "var is >>$R::var<<\n";

package R;
print "R is >>$R<<\n";
print "var is >>$var<<\n";

[download]
Whoops, errors. $R is unavailable in both main:: and R::, while $var is unavailable in main::. Here's how to fix that: 
#!/usr/bin/perl -w
use strict;
{
package R;
my $R = 10;
use vars qw( $var );
$var = 20;
}
package main;
# print "R is >>$R<<\n";
print "var is >>$R::var<<\n";
package R;
# print "R is >>$R<<\n";
print "var is >>$var<<\n";

[download]
There's no way to get to $R, so we'll comment it out. Lexical (or my) variables have block scope, if they're in a block, or file-scope, if they're not. That's why the first example worked, in the main package. (Yes, I put those braces in there just for this point.)

Variables declared with 'use vars' have package scope, so we can switch to package R again and print $var without prepending the package name, as we have to do when we're in package main. Presumably the new our works much the same way in 5.6.

I can't let the idea of lexical variables and scope go away without making at least one comment about the misunderstood and feared closure. Take a look at this: 

#!/usr/bin/perl -w
use strict;

{
package R;
my $R = 10;
use vars qw( $var );
$var = 20;
sub show_R { $R };
}

package main;
print "var is >>$R::var<<\n";
print "var is ", R::show_R(), "\n";

package R;
print "var is >>$var<<\n";
print "var is ", show_R(), "\n";

[download]
Nifty, hmm? Because $R is available in the same scope where show_R() is defined, the subroutine has access to it, even when called outside of that scope. That's all a closure is, but that's not all it's good for.

In reply to Re: Benchmark.pm's scoping behavior by chromatic
in thread Benchmark.pm's scoping behavior by Russ

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