CS 390 Software Engineering Lecture 6 Ruby

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1 CS 390 Software Engineering Lecture 6 Ruby References: Ruby in Twenty Minutes, available at

2 Outline Clone Ruby example git repository $ git clone ssh://[user@]csserver.evansville.edu/usr/local/git/ruby-examples.git Install RVM (Ruby Version Manager). Use to install consist version of Ruby and Rails See rvm-installation file Ruby 2

3 Ruby Ruby is a scripting language, not unlike Python or PHP. Ruby can be run interactively using the irb (Interactive Ruby) interpreter. It evaluates expressions and prints out results. (puts is a command that outputs a string.) irb(main):001:0> "Hello World" => "Hello World" irb(main):002:0> puts "Hello World" Hello World irb(main):003:0> 3+2 => 5 irb(main):004:0> Math.sqrt(9) => 3.0 3

4 Functions Ruby functions are defined using reserved word def and end with reserved word end. irb(main):010:0> def hi irb(main):011:1> puts "Hello World!" irb(main):012:1> end => :hi Functions may be called with or without parentheses. E.g., using hi or hi(). 4

5 Parameters Ruby parameters are listed in parentheses. They are referenced using #{<param>} irb(main):015:0> def hi(name) irb(main):016:1> puts "Hello #{name}!" irb(main):017:1> end => :hi irb(main):018:0> hi("matz") Hello Matz! 5

6 Parameters Ruby parameters can have default values. Functions with parameters may be called without parentheses as long as it is obvious what is being done. irb(main):019:0> def hi(name = "World") irb(main):020:1> puts "Hello #{name.capitalize}!" irb(main):021:1> end => :hi irb(main):022:0> hi "chris" Hello Chris! irb(main):023:0> hi Hello World! 6

7 Classes Object types are defined using reserved word class and end with reserve word end. Data attribute names are prefixed and are private. irb(main):024:0> class Greeter irb(main):025:1> irb(main):026:2> irb(main):027:2> irb(main):028:1> irb(main):029:2> irb(main):030:2> irb(main):031:1> irb(main):032:2> irb(main):033:2> irb(main):034:1> end => :say_bye def initialize(name = "World") = name def say_hi end puts "Hi #{@name}!" def say_bye end puts "Bye #{@name}, come back soon." 7

8 Instantiation Ruby objects are instantiated using reserved method new that is a class method that calls the class' initialize method. irb(main):035:0> greeter = Greeter.new("Pat") => irb(main):036:0> greeter.say_hi Hi Pat! irb(main):037:0> greeter.say_bye Bye Pat, come back soon. 8

9 Attribute accessors Attributes can be made accessible using attr_accessor. Ruby classes can be opened after definition and new methods and accessors can be added. irb(main):044:0> class Greeter irb(main):045:1> irb(main):046:1> end => Nil attr_accessor :name irb(main):047:0> greeter = Greeter.new("Andy") => irb(main):050:0> greeter.say_hi Hi Andy! irb(main):051:0> greeter.name="betty" => "Betty" irb(main):053:0> greeter.name => "Betty" irb(main):054:0> greeter.say_hi Hi Betty! 9

10 Ruby scripts Look at ri20min.rb. First line is #!/usr/bin/env ruby Comments start with # to the end of the line Start of "main program" is if FILE == $0 to the reserved word end. FILE is an environment variable set to the name of this file. $0 is the first command-line argument (i.e. argv[0]). If they are the same, then this file is being run as a program. Otherwise it is being used as a library and this code is ignored. Run script using: ruby ri20min.rb 10

11 Ruby objects A Ruby object has Smalltalk-like behavior and can be asked if it responds to a particular method name. E.g., this can be used to distinguish between single objects and collection objects. Collections have many methods such as each and join. 11

12 Arrays Arrays can be defined explicitly giving a list in [ ]. mg.names = ["Albert", "Brenda", "Charles", "Dave", "Engelbert"] 12

Overview of the Ruby Language. By Ron Haley

Overview of the Ruby Language. By Ron Haley Overview of the Ruby Language By Ron Haley Outline Ruby About Ruby Installation Basics Ruby Conventions Arrays and Hashes Symbols Control Structures Regular Expressions Class vs. Module Blocks, Procs,