Modules and Packages

Package Variables

our declares a package variable that package subroutines can share.

package variable A package variable belongs to a package namespace and can be referenced with a qualified name.

Package Variables

amount
package_variables.pl
Replay: real traced execution (multi-file project)
use strict;
use warnings;

package Counter;

our $total = 0;

sub add {
    my ($amount) = @_;
    $total = $total + $amount;
    return $total;
}

package main;

my $amount = 4;
my $first = Counter::add($amount);
my $second = Counter::add(2);

print "amount=$amount\n";
print "first=$first\n";
print "second=$second\n";

use strict;
use warnings;

package Counter;

our $total = 0;

sub add {
    my ($amount) = @_;
    $total = $total + $amount;
    return $total;
}

package main;

my $amount = 1;
my $first = Counter::add($amount);
my $second = Counter::add(2);

print "amount=$amount\n";
print "first=$first\n";
print "second=$second\n";

use strict;
use warnings;

package Counter;

our $total = 0;

sub add {
    my ($amount) = @_;
    $total = $total + $amount;
    return $total;
}

package main;

my $amount = 7;
my $first = Counter::add($amount);
my $second = Counter::add(2);

print "amount=$amount\n";
print "first=$first\n";
print "second=$second\n";

  1. $total ← 0, $amount ← 4

    6our $total→ 0 = 0;78sub add {9    my ($amount) = @_;10    $total = $total + $amount;11    return $total;12}1314package main;1516my $amount→ 4 = 4; #@amount=1, 717my $first = Counter::add($amount4);18my $second = Counter::add(2);

  2. $amount ← 4, $total ← 4

    pass 1 of 2
    8sub add {9    my ($amount→ 4) = @_;10    $total→ 4 = $total + $amount4;11    return $total4;12}

  3. $first ← 4

    16my $amount = 4; #@amount=1, 717my $first→ 4 = Counter::add($amount4);18my $second = Counter::add(2);

  4. $amount ← 2, $total ← 6

    pass 2 of 2
    8sub add {9    my ($amount→ 2) = @_;10    $total→ 6 = $total + $amount2;11    return $total6;12}

  5. $second ← 6

    17my $first = Counter::add($amount);18my $second→ 6 = Counter::add(2);1920print "amount=$amount4\n";21print "first=$first4\n";22print "second=$second6\n";
    outputamount=4
first=4
second=6

  1. $total ← 0, $amount ← 1

    6our $total→ 0 = 0;78sub add {9    my ($amount) = @_;10    $total = $total + $amount;11    return $total;12}1314package main;1516my $amount→ 1 = 1;17my $first = Counter::add($amount1);18my $second = Counter::add(2);

  2. $amount ← 1, $total ← 1

    pass 1 of 2
    8sub add {9    my ($amount→ 1) = @_;10    $total→ 1 = $total + $amount1;11    return $total1;12}

  3. $first ← 1

    16my $amount = 1;17my $first→ 1 = Counter::add($amount1);18my $second = Counter::add(2);

  4. $amount ← 2, $total ← 3

    pass 2 of 2
    8sub add {9    my ($amount→ 2) = @_;10    $total→ 3 = $total + $amount2;11    return $total3;12}

  5. $second ← 3

    17my $first = Counter::add($amount);18my $second→ 3 = Counter::add(2);1920print "amount=$amount1\n";21print "first=$first1\n";22print "second=$second3\n";
    outputamount=1
first=1
second=3

  1. $total ← 0, $amount ← 7

    6our $total→ 0 = 0;78sub add {9    my ($amount) = @_;10    $total = $total + $amount;11    return $total;12}1314package main;1516my $amount→ 7 = 7;17my $first = Counter::add($amount7);18my $second = Counter::add(2);

  2. $amount ← 7, $total ← 7

    pass 1 of 2
    8sub add {9    my ($amount→ 7) = @_;10    $total→ 7 = $total + $amount7;11    return $total7;12}

  3. $first ← 7

    16my $amount = 7;17my $first→ 7 = Counter::add($amount7);18my $second = Counter::add(2);

  4. $amount ← 2, $total ← 9

    pass 2 of 2
    8sub add {9    my ($amount→ 2) = @_;10    $total→ 9 = $total + $amount2;11    return $total9;12}

  5. $second ← 9

    17my $first = Counter::add($amount);18my $second→ 9 = Counter::add(2);1920print "amount=$amount7\n";21print "first=$first7\n";22print "second=$second9\n";
    outputamount=7
first=7
second=9