Package-Based Object Patterns

Package Calls

Pass a current value into a package routine and receive an updated value.

package-calls A package routine can receive state, perform work, and return the result.

Package Calls

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

package Counter;

sub add {
    my ($value, $step) = @_;
    return $value + $step;
}

package main;

my $step = 3;
my $start = 10;
my $next = Counter::add($start, $step);

print "start=$start\n";
print "step=$step\n";
print "next=$next\n";

use strict;
use warnings;

package Counter;

sub add {
    my ($value, $step) = @_;
    return $value + $step;
}

package main;

my $step = 1;
my $start = 10;
my $next = Counter::add($start, $step);

print "start=$start\n";
print "step=$step\n";
print "next=$next\n";

use strict;
use warnings;

package Counter;

sub add {
    my ($value, $step) = @_;
    return $value + $step;
}

package main;

my $step = 5;
my $start = 10;
my $next = Counter::add($start, $step);

print "start=$start\n";
print "step=$step\n";
print "next=$next\n";

  1. $step ← 3, $start ← 10

    13my $step→ 3 = 3; #@step=1, 514my $start→ 10 = 10;15my $next = Counter::add($start10, $step3);

  2. $value ← 10, $step ← 3

    6sub add {7    my ($value→ 10, $step→ 3) = @_;8    return $value10 + $step3;9}

  3. $next ← 13

    14my $start = 10;15my $next→ 13 = Counter::add($start10, $step3);1617print "start=$start10\n";18print "step=$step3\n";19print "next=$next13\n";
    outputstart=10
step=3
next=13

  1. $step ← 1, $start ← 10

    13my $step→ 1 = 1;14my $start→ 10 = 10;15my $next = Counter::add($start10, $step1);

  2. $value ← 10, $step ← 1

    6sub add {7    my ($value→ 10, $step→ 1) = @_;8    return $value10 + $step1;9}

  3. $next ← 11

    14my $start = 10;15my $next→ 11 = Counter::add($start10, $step1);1617print "start=$start10\n";18print "step=$step1\n";19print "next=$next11\n";
    outputstart=10
step=1
next=11

  1. $step ← 5, $start ← 10

    13my $step→ 5 = 5;14my $start→ 10 = 10;15my $next = Counter::add($start10, $step5);

  2. $value ← 10, $step ← 5

    6sub add {7    my ($value→ 10, $step→ 5) = @_;8    return $value10 + $step5;9}

  3. $next ← 15

    14my $start = 10;15my $next→ 15 = Counter::add($start10, $step5);1617print "start=$start10\n";18print "step=$step5\n";19print "next=$next15\n";
    outputstart=10
step=5
next=15