General Purpose Language Ruby Kit Chan COMP3351 Programming Languages November 9, 2007

Outline Reference Reference Introduction Introduction Ruby is Ruby is Features Features Array Array Loop Loop Ruby v.s. Java Ruby v.s. Java Duck Typing Duck Typing Dynamic Typing Dynamic Typing Type Tag Checking Type Tag Checking Functional Programming Functional Programming

Reference Wikipedia Wikipedia Ruby Official Website Ruby Official Website Learning Ruby Learning Ruby Duck Typing Duck Typing

Introduction Developed by Yukihiro “Matz” Matsumoto, in Feb, 1993 Developed by Yukihiro “Matz” Matsumoto, in Feb, 1993 First released in 1995 First released in Ruby 1.9 developed March, Ruby 1.9 developed March, 2007 Named Named As a gemstone because of a joke with in Matsumoto’s friends alluding to Perl’s name As a gemstone because of a joke with in Matsumoto’s friends alluding to Perl’s name

Ruby is Cross-platform Operating System Cross-platform Operating System Combines syntax by Combines syntax by Perl Perl Smalltalk-like OO features Smalltalk-like OO features Shares features with Shares features with Lisp Lisp Python Python Dylan Dylan CLU CLU

Ruby is The interpreted scripting language for The interpreted scripting language for Quick Quick Easy OO programming Easy OO programming designed for programmer productivity designed for programmer productivity Straight-forward Straight-forward principle of least surprise (POLS) principle of least surprise (POLS) Ruby behaves in a way that minimizing confusion for experienced users Ruby behaves in a way that minimizing confusion for experienced users After you learn Ruby very well After you learn Ruby very well

Ruby is Obedient Obedient>> 'Hello World' => "Hello World” >> 'blink ' * 4 >> 'blink ' * 4 => "blink blink blink blink " => "blink blink blink blink " Your Calculator Your Calculator>> 1+1 => 2 Or>> 2**2**2 => 16

Features Object-oriented Object-oriented Four levels of variables: Four levels of variables: Global$var Global$var Local[a-z] or _; var Local[a-z] or _; var Constant[A-Z] Constant[A-Z] Exception handling Exception handling Iterators & closures Iterators & closures Automatic garbage collecting Automatic garbage collecting Highly portable Highly portable

Array >> numbers = ["zero", "one", "two", "three", "four"] >> numbers = ["zero", "one", "two", "three", "four"] => ["zero", "one", "two", "three", "four"] => ["zero", "one", "two", "three", "four"] => Array => Array >> numbers[0] >> numbers[0] => "zero" => "zero" What arrays do? >> numbers[0].class >> numbers[0].class => String => String >> numbers[0].upcase >> numbers[0].upcase => "ZERO" => "ZERO" >> numbers[0].reverse >> numbers[0].reverse => "orez" => "orez"

Loop If I knew Ruby when I was in grade school……. If I knew Ruby when I was in grade school……. >> 100.times do >> 100.times do.. puts "I won't do that again".. puts "I won't do that again".. end.. end I won't do that again I won't do that again => 100 => 100 My life was going to be much easier My life was going to be much easier

Ruby v.s. Java- Syntax begin_time = Time.now.to_i begin_time = Time.now.to_i i = 0 i = times do 100.times do i += 1 i += 1 j = 0 j = 0 10.times do 10.times do j += 1 j += 1 k = 0 k = times do 100.times do k += 1 k += 1 puts i.to_s + " + " + j.to_s + " + " + k.to_s puts i.to_s + " + " + j.to_s + " + " + k.to_s end end end_time = Time.now.to_i end_time = Time.now.to_i difference = end_time - begin_time difference = end_time - begin_time puts "It took " + difference.to_s + " seconds" puts "It took " + difference.to_s + " seconds" ho = gets ho = gets class test { public static void main(String[] args) { long startTime = System.currentTimeMillis(); for (int i=0; i<=100 ; i++ ) { for (int j=0; j<=10 ; j++) { for (int k=0; k<=100 ; k++ ) { System.out.println( i + " + " + j + " + " + k);}}} long endTime = System.currentTimeMillis(); long difference = (endTime - startTime)/1000; System.out.println("It took " + difference + " seconds"); }

Ruby v.s. Java Performance Performance Ruby: 24 – 26 seconds Ruby: 24 – 26 seconds Java: 1 – 2 seconds Java: 1 – 2 seconds LanguageParadigmTypeChecking Java Imperative Imperative Object-oriented Object-oriented Generic GenericStatic Ruby Imperative Imperative Object-oriented Object-oriented Functional Functional Aspect-oriented Aspect-orientedDynamic(duck)

Duck Typing Ruby interpreter is happy to treat it as it were a duck Ruby interpreter is happy to treat it as it were a duck If an object walks and talks like a duck If an object walks and talks like a duck Duck typing means Duck typing means An object type is defined by what it can do An object type is defined by what it can do Not by what it is Not by what it is Duck typing refers to Duck typing refers to less concerned with the class of an object less concerned with the class of an object more concerned with what methods can be called on it more concerned with what methods can be called on it what operations can be performed what operations can be performed

Duck Typing we use respond_to? we use respond_to? Example Example >> puts ('A string'.respond_to? :to_str) >> puts ('A string'.respond_to? :to_str) true true => nil => nil >> puts (Exception.new.respond_to? :to_str) >> puts (Exception.new.respond_to? :to_str) true true => nil => nil If an object quacks like a duck, just treat it as a duck…. If an object quacks like a duck, just treat it as a duck…. We should treat objects to the methods they define We should treat objects to the methods they define

Duck Typing >> class Duck >> class Duck.. def quack.. def quack.. 'Quack!'.. 'Quack!'.. end.. end.. def swim.. def swim.. 'Paddle paddle paddle...'.. 'Paddle paddle paddle...'.. end.. end => nil => nil >> class Goose >> class Goose.. def honk.. def honk.. 'Honk!'.. 'Honk!'.. end.. end.. def swim.. def swim.. 'Splash splash splash...'.. 'Splash splash splash...'.. end.. end => nil => nil >> >>

Duck Typing >> class DuckRecording >> class DuckRecording.. def quack.. def quack.. play.. play.. end.. end.. def play.. def play.. 'Quack'.. 'Quack'.. end.. end => nil => nil >> def make_it_quack(duck).. duck.quack.. end => nil >> puts make_it_quack(Duck.new) Quack! >> puts make_it_quack(DuckRecording.new) Quack => nil >> def make_it_swim(duck).. duck.swim.. end => nil >> puts make_it_swim(Duck.new) Paddle paddle paddle... => nil >> puts make_it_swim(Goose.new) Splash splash splash... => nil

Add Method to Class Instances Add methods to individual class instances Add methods to individual class instances class Duck class Duck def quack def quack puts 'Quack!' puts 'Quack!' end end def swim def swim puts 'Paddle paddle paddle...' puts 'Paddle paddle paddle...' end end d = Duck.new #create new instance of the class d = Duck.new #create new instance of the class d.quack#call method d.quack#call method d.swim#call method d.swim#call method def d.walk#override existing method with def d.walk#override existing method with #new functionality puts 'I am walking... walking' puts 'I am walking... walking' end end d.walk d.walk => nil => nil => # => # Quack! Quack! => nil => nil Paddle paddle paddle... Paddle paddle paddle... => nil => nil I am walking... walking I am walking... walking => nil => nil irb(main):022:0> irb(main):022:0>

Dynamic Typing Ruby, the data types are not wholly declared on variable Ruby, the data types are not wholly declared on variable Data associated with variables are not known until the time of execution Data associated with variables are not known until the time of execution Advantage: Advantage: flexibility flexibility Less work for the programmer Less work for the programmer

Type Tag Checking Ruby is dynamically typed Ruby is dynamically typed it supports run-time dispatch on tagged data it supports run-time dispatch on tagged data Takes place at run-time Takes place at run-time values bound in variables can acquire different tags depending on the execution path values bound in variables can acquire different tags depending on the execution path

Example var x #declares the name x var x #declares the name x x :=1#associates int val 1 to name x x :=1#associates int val 1 to name x x :=“hi”#associates the string val “hi” to name x x :=“hi”#associates the string val “hi” to name x ……………illegal ……………illegal binding x to values of inconsistent type binding x to values of inconsistent type Pure Dynamically typed system allows the execution Pure Dynamically typed system allows the execution Type tags are attached to values Type tags are attached to values Dynamic typing catches errors during program execution Dynamic typing catches errors during program execution

Example......cont Dynamic typing keeps all program values “tagged” Dynamic typing keeps all program values “tagged” Checks the tag before using any value in an operation Checks the tag before using any value in an operation var x :=1 #binds val 1 to x var x :=1 #binds val 1 to x var y := “hi”#binds val “hi” to y var y := “hi”#binds val “hi” to y var z := x + y#add x to y var z := x + y#add x to y

Example......cont The value bound to x be a pair (integer, 1) The value bound to x be a pair (integer, 1) The value bound to y be a pair (string, “hi”) The value bound to y be a pair (string, “hi”) Attempts to execute the 3 rd line, Attempts to execute the 3 rd line, Checks the type tags integer and string Checks the type tags integer and string If the operation + (addition) is not defined If the operation + (addition) is not defined An error is signaled An error is signaled

Why Ruby? High productivity for programmers High productivity for programmers Execution time is not the main concern Execution time is not the main concern Web Developments Web Developments Projects like Ruby on Rails Projects like Ruby on Rails Functional Programming Functional Programming Paradigm treats computation as the evaluation of mathematical functions Paradigm treats computation as the evaluation of mathematical functions Emphasize on application of functions Emphasize on application of functions Largely being used in academia Largely being used in academia Lambda calculus Lambda calculus Forms the foundation for most models of functional programming Forms the foundation for most models of functional programming

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