does the scope of array reference matter in this sample code - perl

Question

#!/usr/bin/perl
A();
B();
sub A {
my #array = qw(value_1 value_2);
$array_ref = \#array;
}
sub B {
foreach my $i ( #{$array_ref} ) {
print "Array Value: $i \n";
}
}
Since the array is declared using the 'my' keyword, could the array reference be lost ?
Can any one brief me over this.

Answer 1

No, the scope of the variable expires, but not the memory address. The data will remain.
Isn't this something you could have simply tried? =) I just copy/pasted your code and tried it, and it worked fine.
For proper encapsulation, though, you really should return the array ref instead:
B(A());
# Or
my $aref = A();
B($aref);
sub A {
my #array = qw(value_1 value_2);
return \#array;
}
sub B {
my $array_ref = shift;
foreach my $i ( #$array_ref ) {
print "Array Value: $i \n";
}
}

Answer 2

I definitely recommend using
use strict;
in Perl scripts (put it on the very beginning). In this very case it will complain about $array_ref being undeclared global. And it is likely the main source of the confusion: you use $array_ref without declaring it in any way, so it is treated as a global variable.
The array content itself is kept because it is referenced by this very variable so reference count remains greater than 0 (perl uses reference counting internally to keep track of when to remove variables).
Of course approach like shown in TLP posts (without globals) is to be recommended.

Answer 3

Actually there is a very good reason to use my in this example.
You actually want the variable to be re-created every time through the subroutine, otherwise you would change the values that you got earlier.
use strict;
use warnings;
use 5.10.1;
my #array;
sub A{
push #array, scalar #array; # add the length of #array to the end
return \#array;
}
my #list;
for( 'A'..'D' ){
my $current = A();
push #list, $current;
say join ' ', #$current;
}
say '';
say join ' ', #$_ for #list;
0
0 1
0 1 2
0 1 2 3
0 1 2 3
0 1 2 3
0 1 2 3
0 1 2 3
Notice how every copy of #array is identical.
This is why you need a new copy for every time the subroutine is called.
use strict;
use warnings;
use 5.10.1;
sub A{
state $iter = 0;
my #array;
push #array, 0..$iter++;
return \#array;
}
my #list;
for( 'A'..'D' ){
my $current = A();
push #list, $current;
say join ' ', #$current;
}
say '';
say join ' ', #$_ for #list;
0
0 1
0 1 2
0 1 2 3
0
0 1
0 1 2
0 1 2 3