Ruby Objects

--Sowjanya Mudunuri

References

• The Ruby Programming Language by David Flanagan and Yukihiro Matsumoto

• Beginning Ruby by Peter Cooper

• Disclaimer: This notes is composed from the above referenced books. This presentation is used to help fellow friends who are trying to learn ruby.

Ruby Objects

• All Values are objects in Ruby

• Ruby is a strictly object oriented language

• when we work with objects in ruby we are really working with object references

p = “Cloud”

we are storing a reference to the String object “Cloud” into p

Passing Objects by reference & the Object lifetime

• When we pass an object to a method in Ruby, it is an object reference that is passed to the method

• When ‘new’ is called on a class it allocates memory to hold an instance of the class and initializes the state of the newly created object by calling the ‘initialize’ method

• Ruby Objects never need to be explicitly deallocated

• Garbage Collection: Ruby automatically destroys objects that are no longer needed( there are no references to the object)

Object_ids

• Every object has an object identifier, a Fixnum, that you can obtain with the object_idmethod

• The value returned by object_id is constant and unique for the lifetime of the object

p = “Hello”

p.object_id

Object Equality

• equal? method is defined by Object class to test whether two values refer to the exact same object

• Most standard ruby classes define the == operator

• Example: Array, Hash, String classes define their == operator to make sense

a = “MyName”

b = “MyName”

a.equal?(b) returns false

a == b returns true

a.object_id

b.object_id

Defining your own == operator

class Point

attr_accessor :x, :y

def initialize(x,y)

@x = x

@y = y

end

def ==(other)

if other.is_a?(Point)

@x==other.x && @y==other.y

else

false

end

end

end

Object Conversion

• Ruby classes define methods that return a representation of the object as a value of a different class

• Examples: to_s , to_i, to_f, to_a

• Defining your own to_s methodclass Point

attr_accessor :x, :y

def to_s

“#{@x}, #{@y}”

end

end

Exercise Time!!

• Define a class named ‘Player’ and have an attribute named ‘name’ and ‘rank’

• Define the == operator on the ‘Player’ by checking the equality of ‘name’ and ‘rank’

• Define a to_s instance method on the ‘Player’ that returns “I am Sowjanya and my rank is 1” where ‘Sowjanya’ and ‘1’ needs to be string interpolated from name and rank attributes

• Well if you are confused about string interpolation now is the time to read about it :: Google ‘string interpolation in ruby’

Exercise Time!!

• Define a class named “Game” with attributes ‘name’ , ‘players’

• Instantiate a ‘Game’ by passing in the name and players and store it the variable ‘game’ Note: Players are an array of Player objects from your previous exercise

• get the object_id of ‘game’

• define a method that iterates through each player and prints it. Note: you can iterate through an array using ‘each’ operator go google it.