Hi !

pronounced as-

SHI-FU SHI-FA

( master shifu from Kung fu Panda ) ( newbie programmer )

=ZEAL

"Mercator projection SW" by Strebe - Own work. Licensed under Creative Commons Attribution-Share Alike 3.0 via Wikimedia Commons

9000 miles

Design Patterns in Ruby

- shifa khan

Design Patterns in Ruby

Design PatternsTried and tested solutions that a programmer can use to solve common problems encountered when designing an application or system.

Why ?

Yay! I’ve finally created

a circular friction reduction

device that is intended to

rotate on a central axial

bearing to transfer load

over distances

. .

Er.. You mean a Wheel?

Knowledge of design patterns helps you recognize frequent patterns in problems and

reuse proven solutions to solve them.

better code , less effort , less time

Smart Programmer

Smart Programmers

Smart Team

Discussions are like :“Hey, lets use an observer for this

function”

Instead of: “Lets add a function in class A to alert class B if property x of an

object of class A exceeds the

threshold value . . .”

Knowledge of design patterns also helps you form a vocabulary for communicating design

decisions among the team during development.

Especially during pair-programming, and other Agile processes, where design is a shared activity.

talk less, communicate better, quick decisions, faster development

How ?

Singleton

TemplateComposite

Observer

Strategy

Iterator

CommandAdapter

Proxy

Decorator

Factory

Builder

Singleton

Observer

require ‘singleton’

require ‘observer’

Strategy

Strategy

-> Implemented when a part of the algorithmvaries, but the context remains same.

-> Step 3 of a 5-step process variesdepending on runtime values, everythingelse remains same.

General Idea

class StudentReport def initialize @grades = Hash.new @name end

def add_name(name) @name = name end

def add_grade(subject, grade) @grades[subject] = grade end

def print output = ["Name, #{@name}"] output << ["Subject,Grade"] grades.keys.each do |subject| output << "#{subject},#{@grades[subject]}" end output.join("\n") endend

class HtmlStudentReport def initialize @grades = Hash.new @name end

def add_name(name) @name = name end

def add_grade(subject, grade) @grades[subject] = grade end

def print output = ["<p>Name: #{@name}</p>"] output << "<table><th><td>Subject</td><td>Grade</td></th>" grades.keys.each do |subject| output << "<tr><td>#{subject}</td>" output << "<td>#{@grades[subject]}</td></tr>" end output << "</table>" output.join("\n") endend

class HtmlStudentReport def initialize @grades = Hash.new @name end

def add_name(name) @name = name end

def add_grade(subject, grade) @grades[subject] = grade end

def print output = ["<p>Name: #{@name}</p>"] output << "<table><th><td>Subject</td><td>Grade</td></th>" grades.keys.each do |subject| output << "<tr><td>#{subject}</td>" output << "<td>#{@grades[subject]}</td></tr>" end output << "</table>" output.join("\n") endend

All steps are same

except for print method

Extract the print step from the algorithm

class StudentReport def initialize(print_strategy) @print_strategy = print_strategy.new @grades = Hash.new @name end

def add_name(name) @name = name end

def add_grade(subject, grade) @grades[subject] = grade end

def print puts @print_strategy.print(@name, @grades) endend

Define it within a strategy

Rest of the context remains unchanged

class HTMLStrategy def print(name, grades) output = ["<p>Name: #{name}</p>"] output << "<table><th><td>Subject</td><td>Grade</td></th>" grades.keys.each do |subject| output << "<tr>" output << "<td>#{subject}</td>" output << "<td>#{grades[subject]}</td>" output << "</tr>" end output << "</table>" output.join("\n") endend

Define print within a strategy

class TextStrategy def print(name, grades) output = ["Name, #{@name}"] output << ["Subject,Grade"] grades.keys.each do |subject| output << "#{subject},#{grades[subject]}" end output.join("\n") endend

student_report = StudentReport.new(TextStrategy.new)

student_report = StudentReport.new(HTMLStrategy.new)

student_report.printThe final implementation of the print method is independent of the strategy implementation

OR

Design patterns in Ruby-by Russ Olsen

Thank You !