topical media & game development

[] readme course(s) preface I 1 2 II 3 4 III 5 6 7 IV 8 9 10 V 11 12 afterthought(s) appendix reference(s) example(s) resource(s) _

pattern(s) / matrix / model(s) / resource(s)

methods do not provide the intuiton and the direct access to solutions that work in real life. design patterns are the jewels, the cristals of object oriented design ...

pattern(s) / matrix / model(s) / resource(s)

motivation(s)

take for example a document processing system ...

material - words, images, tables
formatting, layout
online presentation and editing tool

managing composites

problem -- very many items

solution -- flyweight class

managing layout and formatting

problem -- many algorithms

solution -- composer (strategy) class

display item with attributes

problem -- non-uniform attributes

solution -- embed and hide attributes

develop multi-platform tools (1)

problem -- different window toolkits

solution -- employ platform-specific factories

develop multi-platform tools (2)

problem -- offer uniform widget hierarchy

solution -- separate interface from implementation

provide rich functionality

problem -- support commands with undo

solution -- abstract from specific commands

pattern(s) / matrix / model(s) / resource(s)

design patterns

design pattern(s) -- catalogue

a common design vocabulary
documentation and learning aid
an adjunct to existing methods
a target for redesign

see the GOF Design Patterns and the Patterns Homepage

the pattern schema

structure

name - handle

increases design vocabulary

problem - when to apply

explains the problem and the conflict

solution - general arrangement

design, responsibilities, collaborations

consequences - tradeoffs

to understand the costs and benefits

causes for redesign

design for change

creating an object by specifying a class explicitly -- Abstract Factory, Factory Method, Prototype
dependence on specific operations Chain of Responsibilty, Command
dependence on hardware & software platforms -- Abstract Factory, bridge
dependence on object implementation or representation Abstract Factory, Bridge, Memento, Proxy
algorithm dependence -- Builder, Iterator, Strategy, Template Method, Visitor
extending functionality by subclassing -- Bridge, Chain, Composite, Decorator, Observer
tight coupling -- Abstract Factpry, Bridge, Chain of Responsibilities, Command, Facade, Mediator, Observer
inability to alter classes conveniently -- Adaptor, Decorator, Visitor

kinds of patterns

creational patterns -- factory, singleton, ...
structural patterns -- adaptor, composite, bridge, ...
behavioral patterns -- mediator, observer, command, ...

design patterns

creational

factory
singleton
structural
adaptor
bridge
behavioral
strategy
observer

pattern(s) / matrix / model(s) / resource(s)

creational patterns

factory

provide interface for creating family of related or dependent objects without specifying their concrete classes

Example

also known as kit

participants

AbstractFactory, Concrete Factory, Abstract Product, Concrete Product

consequences

isolate concrete classes
makes exchanging product families easy
promotes consistency among products
supporting new kinds of products is difficult

implementation

See GOF

factory method

define interface for creating an object, but let subclass decide which class to instantiate

also know as

virtual constructor

motivation

encapsulates knowledge of which subclass to instantiate

applicability

when a class can not anticpate the class of the objects it creates
to delegate responsibility of object creation

structure

participants

Product, ConcreteProduct, Creator, ConcreteCreator

consequences

provide hooks for subclasses
connects parallel class hierarchies

Factory, Prototype

singleton

ensure a class has only one instance and provide a global point of access

applicability

only one instance of a class
instance must be extendable by subclassing

implementation

     // .h file 
  
     class Singleton {
     public:
  	static Singleton instance();
     protected:  limit access
  	Singleton();
     private:
  	static Singleton* _instance;
     };
  
  
     // .c file
  
     Singleton* Singleton::_instance = 0;
  
     Singleton* Singleton::instance() {
  	if (_instance == 0)
  		_instance = new Singleton();
  	return _instance;
  	}

consequences

coordinate access to a single instance
reduced namespace
permit refinement
permit variable number of instances

etcetera

see GOF

prototype

specify kinds of objects to create using a prototypical instance and create by copying this prototype

motivation

flexibility, reduce number of classes

applicability

when classes to instantiate are specified at runtime
to avoid building a class hierarchy of factories
to reduce static dependencies

participants

Prototype, ConcretePrototype, Client

consequences

adding and removing product types at runtime
specifying new objects by varying value/structure
reduced subclassing
configure an application with classes dynamically see kit.h and dv/tk/kit.c

AbstractFactory versus Prototype

pattern(s) / matrix / model(s) / resource(s)

structural patterns

are concerned with how classes and objects are composed to form larger structures

Pattern Alias Remarks

language mechanisms

inheritance -- class
delegation -- object

adaptor vs bridge

wrapper

adaptor -- resolves inconsistencies between interfaces
bridge -- relates abstraction to ... implementation

Composite vs Decorator vs Proxy

recursive composition

Composite represents structure
Decorator adds responsibilities
Proxy regulates access

pattern(s) / matrix / model(s) / resource(s)

behavioral patterns

communication

deal with algorithms and the assignment of responsibilities between objects

class

template method -- the skeleton of an algorithm
interpreter -- to evaluate expressions

object

composition

mediator -- provides indirection for loose coupling
chain of responsibility -- connect objects to interact
observer -- to handle dependencies

encapsulating behavior

objectify!

strategy -- algorithm
command -- request
state -- object state -> behavioral change
visitor -- to extract behavior from class
iterator -- access and traversal

observer

one-to-many dependencies and notification

structure

consequences

abstract coupling between subject and observer
support for broadcast
deals with unexpected updates

implementation

mapping subjects to observers
observing more than one subject?
who triggers the update - subject or client of subject
dangling references to subject
consistency of subject (before notification)
adding observer-specific update protocols (push / pull)
specifying modifications of interest (aspects)
how to encapsulate update semantics

[] readme course(s) preface I 1 2 II 3 4 III 5 6 7 IV 8 9 10 V 11 12 afterthought(s) appendix reference(s) example(s) resource(s) _

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motivation(s)

take for example a document processing system ...

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managing composites

problem -- very many items

solution -- flyweight class

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managing layout and formatting

problem -- many algorithms

solution -- composer (strategy) class

document.write(' <a href=');if (!slidemode) { document.write('@slide-'); } else { document.write('patterns-collect.html#slide-'); } document.write('x-strategy'); if (!slidemode) document.write('.html');document.write('>');

display item with attributes

problem -- non-uniform attributes

solution -- embed and hide attributes

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develop multi-platform tools (1)

problem -- different window toolkits

solution -- employ platform-specific factories

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develop multi-platform tools (2)

problem -- offer uniform widget hierarchy

solution -- separate interface from implementation

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provide rich functionality

problem -- support commands with undo

solution -- abstract from specific commands

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design patterns

design pattern(s) -- catalogue

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name - handle

problem - when to apply

solution - general arrangement

consequences - tradeoffs

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causes for redesign

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kinds of patterns

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design patterns

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creational patterns

factory

Example

also known as kit

participants

consequences

implementation

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factory method

also know as

motivation

applicability

structure

participants

consequences

related

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singleton

applicability

implementation

limit access

consequences

etcetera

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prototype

motivation

applicability

participants

consequences

related

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structural patterns

structural patterns

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language mechanisms

adaptor vs bridge

Composite vs Decorator vs Proxy