Accessors and mutators aren't specific to OO Perl. The terms are used in any OO language. They are also known as "getters" and "setters". An accessor gives you access to an attribute of an object and a mutator allows you to change (or mutate) the value of an attribute.

In the simple example below, the attribute we are using is called "foo", the accessor is "get_foo" and the mutator is "set_foo".

package Foo;

sub new {
  my $class = shift;
  return bless {}, $class;
}

sub get_foo {
  my $self = shift;

  return $self->{foo};
}

sub set_foo {
  my $self = shift;

  $self->{foo} = shift;
}

1;
[download]

You often see people discussing what a mutator should return. Common ideas include the new value of the attribute (as in this example), the previous value of the attribute and the object itself (to allow chaining of method calls).

Another common approach is to use a single function (which in this example would be called "foo" which acts as both accessor and mutator). It would use the number of arguments to determine what it should do.

sub foo {
  my $self = shift;

  if (@_) { # mutator
    $self->{foo} = shift;
  } else {  # accessor
    return $self->{foo};
  }
}
[download]