Doc 18 Ruby Classes, Containers & Methods

Contents

 

Classes    

Instance Variables    

Attributes    

Class Methods and Variables    

Inheritance    

Access Control    

Operators    

Adding Methods to Existing Classes    

Containers, Blocks & Iterators    

Arrays    

Iterators    

Blocks are Closures    

Proc    

More about Methods    

Expressions    

 

Copyright ©, All rights reserved. 2005 SDSU & Roger Whitney, 5500 Campanile Drive, San Diego, CA 92182-7700 USA. OpenContent ( http://www.opencontent.org/opl.shtml ) license defines the copyright on this document.

 

References

 

Programming Ruby, The Pragmatic Programmers' Guide, Dave Thomas, ISBN 0-9745140-5-5

 

 

Classes

Definition

class NoState

    def hello

        return 'hello'

    end

 

  def increase(x)

    x + 1

  end

end

 

require 'test/unit'

 

class TestExample < Test::Unit::TestCase

  def test_hello

    object = NoState.new

    assert_equal('hello', object.hello )

    assert( 'hello' == object.hello() )

    assert( 2 == object.increase(1)  )

  end

end

 

 

 

Instance Variables

class Book

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 

  def to_s

    "Book: #@title by #{@author} on #{@date}"

  end

end

 

require 'test/unit'

 

class TestExample < Test::Unit::TestCase

  def test_new

    cat = Book.new("Cat", "Me", "1990")

    assert_instance_of(Book, cat)

    assert( "Book: Cat by Me on 1990" == cat.to_s)

    assert_match(/^Book:(\s)*Cat(.)*Me(.)*1990/, cat.to_s)

  end

end

 

 

 

Instance Variable Access

class Book

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 

  def author

    @author

  end

  

  def author=(new_author)

    @author = new_author

  end

end

 

require 'test/unit'

 

class TestExample < Test::Unit::TestCase

  def test_author

    cat = Book.new("Cat", "Me", "1990")

    assert_not_nil( cat)

    assert( 'Me' == cat.author)

    assert( 'Me' == cat.author() )

    cat.author = 'You'

    assert_equal( 'You',  cat.author )

  end

end

 

 

Attributes

class Book

  attr_reader :title, :author, :date

  attr_writer :title

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

end

 

require 'test/unit'

require 'book'

 

class TestExample < Test::Unit::TestCase

  def test_author

    cat = Book.new("Cat", "Me", "1990")

    assert( 'Me' == cat.author)

    assert( 'Cat' == cat.title)

    cat.title = 'Dog'

    assert_equal( 'Dog', cat.title)

    assert_raise(NoMethodError) {cat.author = 'Me'}

  end

end

 

 

Class Methods and Variables

class Book

  @@count = 0

  

  def Book.count

    @@count

  end

  

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

        @@count += 1

    end

end

 

require 'test/unit'

require 'book'

 

class TestExample < Test::Unit::TestCase

  def test_count

 

    assert( Book.count == 0, 'First count')

    cat = Book.new("Cat", "Me", "1990")

    assert( Book.count == 1, 'Second count')

    assert_raise(NoMethodError) {cat.count}

  end

end

 

 

Inheritance

class Book

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 

  def to_s

    "Book: #@title by #{@author} on #{@date}"

  end

end

 

class ElectronicBook < Book

  def initialize(title, author, date, format)

    super(title, author, date)

    @format = format

  end

  def to_s

    super + " in #{@format}"

  end

end

 

 

 

 

Inheritance tests

require 'test/unit'

require 'book'

 

class TestExample < Test::Unit::TestCase

  def test_count

 

    cat = ElectronicBook.new("Cat", "Me", "1990", 'pdf')

    assert_kind_of(Book, cat )

    assert_kind_of(ElectronicBook, cat)

 

    assert( cat.class == ElectronicBook)

    assert_match( mary thom/(.)+1990(.)+pdf$/,  cat.to_s)

 

  end

end

 

 

 

Access Control

 

1. Public methods

Accessible by anyone

2. Protected methods

Accessible by defining class and subclasses

3. Private Methods

Accessible by defining class

 

c lass Foo

        def method1        #default is public

        end

 

    protected

        methods defined here are protected

        def bar

        end

 

    private

        define a bunch of private methods here

    public

        You can have different groups of same access

end

 

 

 

Alternative Access Declaration

 

class Foo

    def method1

    end

 

    def method2

    end

    ....

    public    :method1, method3

    protected    :method2

    private        :method4, method5

end

 

 

 

Singleton

class Singleton

  private_class_method :new

  @@instance = new

  def Singleton.instance

    @@instance

  end

end

 

 

require 'test/unit'

require 'Singleton'

 

class TestSingleton < Test::Unit::TestCase

  def test_unique

    assert_raise(NoMethodError) {Singleton.new}

    assert_kind_of(Singleton, Singleton.instance)

 

    assert_same( Singleton.instance, Singleton.instance)

    assert( Singleton.instance.equal?( Singleton.instance))

    assert( Singleton.instance.object_id ==

                Singleton.instance.object_id)

 

  end

end

 

 

 

Operators

 

class Book

  attr_reader :title

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 

  def <(book)

    return false if book.kind_of(Book)

    title < book.title

  end

end

 

require 'test/unit'

require 'book'

 

class TestExample < Test::Unit::TestCase

  def test_operator

    cat = Book.new("Cat", "Me", "1990")

    dog = Book.new("Dog", "Me", "1990")

    assert( cat < dog)

  end

end

 

 

 

Adding Methods to Existing Classes

class Fixnum

  def foo

    self + 1

  end

end

 

require 'test/unit'

 

class TestAddingMethods < Test::Unit::TestCase

  def test_integer_foo

  

    assert( 1.foo == 2 )

    assert( -45.foo == -44)

  

  end

end

 

 

Adding Methods to an Object

class Book

  attr_reader :title

    def initialize(title, author, date)

        @title = title

        @author = author

        @date = date

    end

 end

 

 

require 'test/unit'

require 'book'

class TestExample < Test::Unit::TestCase

  def test_singelton_method

    cat = Book.new("Cat", "Me", "1990")

    dog = Book.new("Dog", "Me", "1990")

 

    def cat.foo

      5

    end

 

    assert( cat.foo ==5 )

    assert_raise(NoMethodError) {dog.foo}

  end

end

 

 

Containers, Blocks & Iterators

Arrays

a = [1, 2, 3]

b = 1, 2, 3

c = Array.new

d = Array.new(5)

e = Array.new(5) { |k| k*k }

f = Array.new(5) { |k| k*2 + 1 }

g = Array,new( 5, 'cat')

 

 

 

Array Methods

 

Array is a class

stack = Array.new

stack.push(5)

stack.push(4)

stack.push(3)

sorted = stack.sort

 

Listing methods

puts Array.public_instance_methods

 

Adding methods

class Array

  def foo

    'bar'

  end

end

 

puts [2, 1].foo

 

 

Iterators

 

 

 

Iterators

 

 

 

 

Blocks are Closures

x = 3

def test

  x = 1

  puts x

end

 

test

puts x

 

Output

1

3

 

 

x = 3

def test

  x = 1

  yield

end

 

test {puts x}

puts x

 

Output

3

3

 

 

Proc

class ProcSample

  def set_action(&action)

    @action = action

  end

 

  def do_it

    @action.call(self)

  end

end

 

require 'test/unit'

 

class TestExample < Test::Unit::TestCase

  def test_do_it

    a = ProcSample.new

 

    a.set_action {1}

    assert_equal( a.do_it,  1)

    a.set_action {'cat'}

    assert_equal(a.do_it, 'cat')

 

    x = lambda {'dog'}

    a.set_action(&x)

    assert_equal(a.do_it, 'dog')

  end

end

 

 

 

More Proc

 

x = lambda {puts 1}

3.times(&x)

3.times {puts 2}

 

 

More about Methods

 

Default Parameter Values

def default_values(a, b='cat', c='dog')

  "#{a}, #{b}, #{c}"

end

 

puts default_values(1)

 

Variable-Length Argument Lists

def variable_number(a, *b)

  (0..b.length - 1).each {|k| puts b[k]}

end

 

variable_number(1,2, 3,4, 5)

 

Expanding Arrays

def four(a, b, c, d)

  "#{a}, #{b}, #{c}, #{d}"

end

 

x = [1, 2, 3]

puts four(0, *x)

 

 

 

Expressions

 

Assignment

a = b = 1 + 2

a = (b = 1 + 2) + 3

a, b = b, a

 

x = 0

a, b, c = x, (x += 1), (x += 1)

 

a, b = [1, 2, 3, 4]

#a is 1

#b is 2

 

a, *b = [1, 2, 3, 4]

puts b

 

 

 

if

 

x = gets.to_i

 

if x > 12

  y = 6

else

  y = 1

end

puts y

 

y = if x > 12

      6

    else

      1

    end

puts y

 

 

 

More if

if x > 12 then

  y = 6

else

  y = 1

end

 

if x > 12 then y = 6

else y = 1

end

 

if x > 12:

  y = 6

else

  y = 1

end

 

if x > 12: y = 6

else y = 1

end

 

 

 

unless

 

negation of if

unless x <= 12

  y = 1

else

  y = 6

end

 

 

 

for in

 

syntax sugar for each

for x in (3..10)

  puts x

end

 

(3..10).each {|x| puts x}