Introduction to Object Oriented Perl Programming

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Introduction to Object Oriented Perl Programming

• Issac Goldstand
• Mirimar Networks
• www.mirimar.net
• margol_at_mirimar.net

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Function based programming

• Multiple methods in a shared namespace
• Methods fulfill a generic action and require all
  variables to be passed (or global / otherwise in
  scope)
• No repetition of method names in a single
  namespace

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Objects

• Allow us to add somewhat more abstraction to code
• An object represents a chunk of code thats
  logically connected
• Each object has a specific purpose multiple
  objects are placed together like building blocks
• Objects are built by defining classes which
  contain all the logic and expose the user
  interface

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Classes

• Namespace containing all of the private
  information that makes the object work
• Interface is the way users manipulate the object
• Implementation is the private set of functions
  and variables that happens inside

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Interface

• Class name (eg, Ball)
• Methods (eg, throw, catch, bounce)
• Properties (eg, color, type)
• Constructors

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Perl Considerations

• Widely held opinion is that Perl5 object
  capabilities suck
• An object is simply a special reference,
  blessed into a class (read package)
• Any reference can be used, though hashrefs tend
  to be the popular choice
• Perl6 is supposed to improve this

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Simple Ball Class - Constructor

• package MyBall
• sub new
• my protoshift
• my classref(proto) proto
• my self
• bless self,class
• print I blessed self into class\n
• return self

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Simple Ball Class - Property

• sub color
• my selfshift
• if (_at__) self-gtCOLORshift
• print COLOR is , self
• -gtCOLOR,\n
• return self-gtCOLOR

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Simple Ball Class Method

• sub bounce
• my selfshift
• print I bounced the ball.\n
• sub throw
• my selfshift
• print I threw the ,self-gtcolor, ball.\n

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Simple Ball Class Usage

• my ballnew MyBall
• ball-gtbounce
• ball-gtcolor(red)
• ball-gtthrow

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Simple Ball Class Output

• I blessed MyBallHASH(0x182e602) into MyBall
• I bounced the ball.
• COLOR is red
• COLOR is red
• I threw the red ball.

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Inheritance

• Allows classes which share methods to use a
  single code base
• Perl5 allows for inheritance from multiple parent
  objects
• Parent objects marked using _at_ISA array
• _at_ISA must be a package-local definition, and not
  a file-scoped lexical (dont use my)

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Overridden methods

• A subclass can either use the method definition
  defined in the parent class or override it and
  define its own method
• To override, just simply implement the overridden
  method like any other
• To explicitly access a method in the parent
  class, use selfSUPER-gtmethod(_at_args)

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Inheritance example

• Package MyBallBasketBall
• _at_ISAqw(MyBall)
• sub bounce
• print I dribbled the ball.\n
• sub shoot
• my selfshift
• self-gtSUPERthrow()
• print He shoots He scores!!!\n

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Inheritance example - usage

• my bball
• MyBallBasketBall-gtnew
• bball-gtcolor(orange)
• bball-gtbounce
• bball-gtshoot

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Inheritance example Output

• I blessed MyBallBasketBallHASH(0x1f11254)
  into MyBallBasketBall
• COLOR is orange
• I dribbled the ball.
• COLOR is orange
• I threw the orange ball.
• He shoots... He scores!!!

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Summary

• What is Object Oriented Programming?
• How does Perl allow one to create objects?
• Examples of simple objects
• Inheritance

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Whats next?

• Destructors
• Multiple inheritance
• UNIVERSAL object
• Closures as objects
• Using AUTOLOAD to proxy methods

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For more information

• perldoc perltoot Toms Object Orienteted
  Tutorial
• Object Oriented Perl (Damian Conway)
• Many articles out there, but the above should get
  you well covered

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Thank You!

For more information Issac Goldstand
margol_at_mirimar.net http//www.beamartyr.net/ http
//www.mirimar.net/