References and Nested Data

Passing References

A subroutine can receive a reference and read the data it points to.

reference argument A reference argument lets a subroutine work with a shared data structure.

Passing References

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

sub total_points {
    my ($values_ref, $bonus) = @_;
    my $total = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];
    $total = $total + $bonus;
    return $total;
}

my $bonus = 1;
my $values_ref = [2, 4, 6];
my $total = total_points($values_ref, $bonus);

print "bonus=$bonus\n";
print "total=$total\n";

use strict;
use warnings;

sub total_points {
    my ($values_ref, $bonus) = @_;
    my $total = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];
    $total = $total + $bonus;
    return $total;
}

my $bonus = 0;
my $values_ref = [2, 4, 6];
my $total = total_points($values_ref, $bonus);

print "bonus=$bonus\n";
print "total=$total\n";

use strict;
use warnings;

sub total_points {
    my ($values_ref, $bonus) = @_;
    my $total = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];
    $total = $total + $bonus;
    return $total;
}

my $bonus = 3;
my $values_ref = [2, 4, 6];
my $total = total_points($values_ref, $bonus);

print "bonus=$bonus\n";
print "total=$total\n";

  1. $bonus ← 1

    11my $bonus→ 1 = 1; #@bonus=0, 312my $values_ref = [2, 4, 6];13my $total = total_points($values_ref, $bonus1);

  2. $bonus ← 1, $total ← 12

    4sub total_points {5    my ($values_ref, $bonus→ 1) = @_;6    my $total→ 12 = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];7    $total→ 13 = $total + $bonus1;8    return $total13;9}

  3. $total ← 13

    12my $values_ref = [2, 4, 6];13my $total→ 13 = total_points($values_ref, $bonus1);1415print "bonus=$bonus1\n";16print "total=$total13\n";
    outputbonus=1
total=13

  1. $bonus ← 0

    11my $bonus→ 0 = 0;12my $values_ref = [2, 4, 6];13my $total = total_points($values_ref, $bonus0);

  2. $bonus ← 0, $total ← 12

    4sub total_points {5    my ($values_ref, $bonus→ 0) = @_;6    my $total→ 12 = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];7    $total12 = $total + $bonus0;8    return $total12;9}

  3. $total ← 12

    12my $values_ref = [2, 4, 6];13my $total→ 12 = total_points($values_ref, $bonus0);1415print "bonus=$bonus0\n";16print "total=$total12\n";
    outputbonus=0
total=12

  1. $bonus ← 3

    11my $bonus→ 3 = 3;12my $values_ref = [2, 4, 6];13my $total = total_points($values_ref, $bonus3);

  2. $bonus ← 3, $total ← 12

    4sub total_points {5    my ($values_ref, $bonus→ 3) = @_;6    my $total→ 12 = $values_ref->[0] + $values_ref->[1] + $values_ref->[2];7    $total→ 15 = $total + $bonus3;8    return $total15;9}

  3. $total ← 15

    12my $values_ref = [2, 4, 6];13my $total→ 15 = total_points($values_ref, $bonus3);1415print "bonus=$bonus3\n";16print "total=$total15\n";
    outputbonus=3
total=15