Setters and Getters

Let's discuss the use of setters and getters in packages in this lesson.

We'll cover the following

Setters

In order to assign a value to a member variable of an object after it has been instantiated, we define a setter. Let’s implement setter methods for the package Shape to set the name and sides of the shape.

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package Shape;
sub new {     # constructor
   my $class = shift;
   my $self = {
   # member variables
      name  => shift, 
      sides => shift,
   };
   
   bless $self, $class;
   return $self;
}
sub Description {
  my ($self) = @_;
  print "A $self->{name} has $self->{sides} sides.\n";
}
sub setName {
   my ($self, $value) = @_;
   $self->{name} = $value; 
   return $self->{name};
}
sub setSides {
   my ($self, $value) = @_;
   $self->{sides} = $value; 
   return $self->{sides};
}
1;
$Square = new Shape("square", 4);
$Square->Description();
$Square->setName("Triangle");
$Square->setSides("3");
$Square->Description();

Explanation

In the above code snippet, setName and setSides are setter methods for the package Shape.

  • In lines 21-25, the $value variable is used to assign a value to the member variable name. This is essentially done in the line $self->{name} = $value;.

  • In line 38, this setter is called with the argument Triangle to set the name of the $square object to Triangle.

  • Similarly, in lines 27-31, the $value variable is used to assign a value to the member variable sides. This is essentially done in the line $self->{sides} = $value;.

  • In line 39, this setter is called with the argument 3 to set the sides of the $square object to 3.

Getters

In order to retrieve the value from a member variable of an object, we define a getter. Let’s implement getter methods for the package Shape to get the name and sides of the shape.

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package Shape;
sub new {     # constructor
   my $class = shift;
   my $self = {
   # member variables
      name  => shift, 
      sides => shift,
   };
   
   bless $self, $class;
   return $self;
}
sub Description {
  my ($self) = @_;
  print "A $self->{name} has $self->{sides} sides.\n";
}
sub setName {
   my ($self, $value) = @_;
   $self->{name} = $value; 
   return $self->{name};
}
sub setSides {
   my ($self, $value) = @_;
   $self->{sides} = $value; 
   return $self->{sides};
}
sub getName {
   my ($self) = @_;
   return $self->{name};
}
sub getSides {
   my ($self) = @_;
   return $self->{sides};
}
1;
$Square = new Shape("square", 4);
$shapeName = $Square->getName();
$shapeSides = $Square->getSides();
print "Shape name : $shapeName and Shape Sides : $shapeSides";

Explanation

In the above code snippet, getName and getSides are getter methods for the shape package.

  • In lines 33-36, the line return $self->{name}; returns the name of our object.

  • This getter is then called in the line 47, and the value returned is stored in the variable $shapeName.

  • Similarly, in lines 38-41, the line return $self->{sides}; returns the sides of our object.

  • In line 48, this getter is called, and the value returned is stored in the variable $shapeSides.