lecture.md

Day 4:

Intro to Classes

Objective
To be able to create simple classes and methods

Prev Work:

• Common Datatypes
• Loops, Conditionals
• Arrays, Hashes
• functions

Let's talk about

• Instance Variables (attributes)
• Class Variables
• Instance Methods or Object Methods
• Getter Methods
• Setter Methods
• attr_accessor, attr_reader, attr_writer
• self

greet_pc.rb

Create a function called 'greet' that

# takes two arguments:
# name and greeting

# greet(name, greeting) => "#{greeting} #{name}"

greet.rb

def greet(name, greeting)
	puts "#{greeting} #{name}"
end

greets_pc.rb

# Create a method that takes a list of people
# and greets them their greetings

# greets(people, greetings)

greets.rb

people = [Kyle, Del, Jackie]
greetings = ["Hey", "Howdy", "Hi"]

def greets(people, greetings)
	for x in (0..people.length - 1)
		puts "#{greetings[x] #{people[x]}"
	end
end	

greets(people,greetings)		

What happens when we want to start adding people? Then we have to go and also update their 'greeting'.

We could try to make this easier with something called a class

person_class.rb

class Person

	def inititalize(name)
		@name_attribute = name
	end
	
	def say_hello
		"Hello, my name is #{@name_attribute}!"
	end	
	
end


person = Person.new("Jack")
person.say_hello # => "Hello my name is some_name"

What's going on here?

• def initialize(..)

  • creates a new object with the .new(..) method
  • person = Person.new creates an instance of a Person class and assigns it to person.

• @name_attribute

  • the @name_attribute is an instance variable accessible by all the methods in the the object. We say @name_attribute is an 'attribute' of an object.

• say_hello

  • This is a function definition inside the object and is conventionally called a Method.
    • Note: The terms method and function may have been used interchangably before, but method should be used to mean an object's function

Lets Try another example

greeter.rb

class Greeter
	def initialize(people)
		@people = people
	end
	
	def greets
		@people.each do |person, greeting|
			puts "#{greeting} #{person}"
		end
	end
end

people = { "Kyle" => "Hey",
			"Del" => "Howdie",
			"Jackie" => "Hi"}

greeter = Greeter.new(people)

greeter.greets

A gets method

Person_2.rb

class Person
	def initialize(name)
		@name = name
	end

	def name 
		@name
	end
	
end

greeter = Greeter.new
greeter.name

A set method

Person_3.rb

class Person

	def initialize(name)
		@name = name
	end
	
	def name
	  @name
	end
	
	def name=(other)
		@name = name
	end
	
end

person = Person.new("john")
puts person.name

person.name = "mike"
puts person.name

Adding a class Variables

people_4.rb

class Person
   @@num_of_people = 0
   
   def initialize(name)
     @name = name
     @@num_of_people += 1
     puts @@num_of_people
   end
   
   def name
     @name
   end
    
   def name=(other)
     @name = other
   end
   
    
end