protected(3)
NAME
protected - "private" data fields which are inherited by
child classes
SYNOPSIS
package Foo;
use public qw(foo bar );
use private qw(_private);
use protected qw(_pants spoon);
sub squonk {
my($self) = shift;
$self->{_pants} = 'Infinite Trousers';
$self->{spoon} = 'What stirs me, stirs everything';
...
}
package Bar;
# Inherits foo, bar, _pants and spoon
use base qw(Foo);
...
DESCRIPTION
- Protected member.
- Restricted data or functionality. An attribute or
method only directly accessible to methods of the same
class or of a subclass, but inaccessible from any
other scope. - From "Object Oriented Perl" by Damian Conway
- The "protected" module implements something like Protected
data members you might find in a language with a more tra
ditional OO implementation such as C++. - Protected data members are similar to private ones with
the notable exception in that they are inherited by sub
classes. This is useful where you have private informa
tion which would be useful for subclasses to know as well. - For example: A class which stores an object in a database
might have a protected member "_Changed" to keep track of
changes to the object so it does not have to waste time
re-writing the entire thing to disk. Subclasses of this
obviously need a _Changed field as well, but it would be
breaking encapsilation if the author had to remember to
"use fields qw(_Changed)" (Assuming, of course, they're
using fields and not just a plain hash. In which case
forget this whole module.) - The Camel Behind The Curtain
- In reality, there is little difference between a "pro
tected" variable and a "public" on in Perl. The only real
difference is that the protected module doesn't care what
the field is called (ie. if it starts with an underscore
or not) whereas fields uses the name to determine if the
variable is public or private (ie. inherited or not).
AUTHOR
Michael G Schwern <schwern@pobox.com>
SEE ALSO
- public, private, fields, Class::Fields, base