This is the example from the book "Intermediate Perl" and it is the easiest one I could find.
First of all, the final script we want to write is:
use strict;
use horse;
my $tv_horse = horse->named('Mr. Ed');
$tv_horse->set_name("Mister Ed");
$tv_horse->set_color("grey");
print $tv_horse->name, ' is ', $tv_horse->color, "\n";
We can see method invocation, as we have used arrow operator(->). Therefore we can conclude that this script is using APIs from an OO module (A Perl module is a reusable package defined in a library file whose name is the same as the name of the package (with a .pm on the end).). That module is horse.
we can think of above program as written below in non-OO Perl:
Horse::named(Horse, 'Mr. Ed');
$tv_horse::set_name($tv_horse, 'Mister Ed');
$tv_horse::set_color($tv_horse, 'grey');
$tv_horse::name($tv_horse);
Following is explanation of above program line by line :
use strict;
Good for debugging, it is recommended to use.
use horse;
This line is to load the module horse, which has APIs(or Methods) defined or inheriting APIs from another module.
my $tv_horse = horse->named('Mr. Ed');
This line creates a new object instance of horse with name 'Mr. Ed'. named can be thought of as an API, although in Perl we call it as a constructor. It'll be explained when we take a look at horse module.
$tv_horse->set_name("Mister Ed");
This line uses API set_name, which, as name says, sets the name for horse object. It is a good practice to use self explanatory names.
$tv_horse->set_color("grey");
This line also explains itself the functionality.
print $tv_horse->name, ' is ', $tv_horse->color, "\n";
This line is using 2 APIs- name and color. But these are somehow different, we'll see that later.
Now the file horse.pm (Module which was loaded in previous program):
package horse;
use animal;
use strict;
use vars qw(@ISA);
our @ISA = qw(animal);
1;
There are no APIs defined in this package. However it is inheriting APIs from another package 'animal':
@ISA = qw(animal);
This line will give error with use strict . So we have to use line:
use vars qw(@ISA);
In a package we should always return 1.
Now file animal.pm, which contains all APIs:
package animal;
use strict;
sub named
{
my $class = shift;
my $name = shift;
my $self = {
name => $name,
color => $class->default_color
};
bless $self, $class;
}
sub default_color { "brown" }
sub set_name
{
my $self = shift;
$self->{name} = shift;
}
sub set_color
{
my $self = shift;
$self->{color} = shift;
}
sub name
{
my $self = shift;
ref $self ? $self->{name} : $self;
}
sub color
{
my $self = shift;
ref $self ? $self->{color} : $self;
}
1;
if we think of our final script as follows, then it is very simple to write animal.pm:
Horse::named(Horse, 'Mr. Ed');
$tv_horse::set_name($tv_horse, 'Mister Ed');
$tv_horse::set_color($tv_horse, 'grey');
$tv_horse::name($tv_horse);
First of all, the final script we want to write is:
use strict;
use horse;
my $tv_horse = horse->named('Mr. Ed');
$tv_horse->set_name("Mister Ed");
$tv_horse->set_color("grey");
print $tv_horse->name, ' is ', $tv_horse->color, "\n";
We can see method invocation, as we have used arrow operator(->). Therefore we can conclude that this script is using APIs from an OO module (A Perl module is a reusable package defined in a library file whose name is the same as the name of the package (with a .pm on the end).). That module is horse.
we can think of above program as written below in non-OO Perl:
Horse::named(Horse, 'Mr. Ed');
$tv_horse::set_name($tv_horse, 'Mister Ed');
$tv_horse::set_color($tv_horse, 'grey');
$tv_horse::name($tv_horse);
Following is explanation of above program line by line :
use strict;
Good for debugging, it is recommended to use.
use horse;
This line is to load the module horse, which has APIs(or Methods) defined or inheriting APIs from another module.
my $tv_horse = horse->named('Mr. Ed');
This line creates a new object instance of horse with name 'Mr. Ed'. named can be thought of as an API, although in Perl we call it as a constructor. It'll be explained when we take a look at horse module.
$tv_horse->set_name("Mister Ed");
This line uses API set_name, which, as name says, sets the name for horse object. It is a good practice to use self explanatory names.
$tv_horse->set_color("grey");
This line also explains itself the functionality.
print $tv_horse->name, ' is ', $tv_horse->color, "\n";
This line is using 2 APIs- name and color. But these are somehow different, we'll see that later.
Now the file horse.pm (Module which was loaded in previous program):
package horse;
use animal;
use strict;
use vars qw(@ISA);
our @ISA = qw(animal);
1;
There are no APIs defined in this package. However it is inheriting APIs from another package 'animal':
@ISA = qw(animal);
This line will give error with use strict . So we have to use line:
use vars qw(@ISA);
In a package we should always return 1.
Now file animal.pm, which contains all APIs:
package animal;
use strict;
sub named
{
my $class = shift;
my $name = shift;
my $self = {
name => $name,
color => $class->default_color
};
bless $self, $class;
}
sub default_color { "brown" }
sub set_name
{
my $self = shift;
$self->{name} = shift;
}
sub set_color
{
my $self = shift;
$self->{color} = shift;
}
sub name
{
my $self = shift;
ref $self ? $self->{name} : $self;
}
sub color
{
my $self = shift;
ref $self ? $self->{color} : $self;
}
1;
if we think of our final script as follows, then it is very simple to write animal.pm:
Horse::named(Horse, 'Mr. Ed');
$tv_horse::set_name($tv_horse, 'Mister Ed');
$tv_horse::set_color($tv_horse, 'grey');
$tv_horse::name($tv_horse);
