The class

This is a very simple class-definition. The new method will receive the name of the class as the first parameter and use bless to create a instance of the class.

It also defines a method called DESTROY that will be called when the instance is destroyed.

The interesting thing is that you can define the DESTROY function either as a regular function:

sub DESTROY {
}

or even without the sub keyword:

DESTROY {
}

examples/MyZorg.pm

package MyZorg;
use strict;
use warnings;

sub new {
    my ($class) = @_;
    print "Inside new for $class\n";
    return bless {}, $class;
}

DESTROY {
    my ($self) = @_;
    print "DESTROY for: $self\n";
}

1;

Call destructor when leaving scope

examples/show_destructor_scope.pl

use strict;
use warnings;
use MyZorg;

print "Before calling new\n";

{
    my $zorg = MyZorg->new;
    print "Instance of: $zorg\n";
    print "Before leaving scope\n";
}

print "After leaving scope\n";

Run it like this:

perl -I. show_destructor_scope.pl

The output is this:

Before calling new
Inside new for MyZorg
Instance of: MyZorg=HASH(0x55fa4be06470)
Before leaving scope
DESTROY for: MyZorg=HASH(0x55fa4be06470)
After leaving scope

Call destructor when changing variable content

If we assign some new value to the only variable that refers to this object, then to it is destroyed.

examples/show_destructor_reset.pl

use strict;
use warnings;
use MyZorg;

print "Before calling new\n";

my $zorg = MyZorg->new;
print "Instance of: $zorg\n";
print "Before changing variable\n";

$zorg = 'something else';

print "After changing variable\n";

Run:

perl -I. show_destructor_reset.pl

Output:

Before calling new
Inside new for MyZorg
Instance of: MyZorg=HASH(0x55a3d0686470)
Before changing variable
DESTROY for: MyZorg=HASH(0x55a3d0686470)
After changing variable

Call destructor when program ends

The destructor is also called when we reach the end of our program.

examples/show_destructor_eof.pl

use strict;
use warnings;
use MyZorg;

print "Before calling new\n";

my $zorg = MyZorg->new;
print "Instance of: $zorg\n";

Run:

perl -I. show_destructor_eof.pl

Output:

Before calling new
Inside new for MyZorg
Instance of: MyZorg=HASH(0x5580a0843470)
DESTROY for: MyZorg=HASH(0x5580a0843470)

Call destructor before the END blocks

Perl allows you to create END blocks (or END functions) that will be called at the very end of running the program. The END blocks will be called after all the destructor were called.

examples/show_destructor_end.pl

use strict;
use warnings;
use MyZorg;

print "Before calling new\n";

END {
    print "END\n";
}

my $zorg = MyZorg->new;
print "Instance of: $zorg\n";

Run:

perl -I. show_destructor_end.pl

Output:

Before calling new
Inside new for MyZorg
Instance of: MyZorg=HASH(0x561971eb1470)
DESTROY for: MyZorg=HASH(0x561971eb1470)
END