The difference between Ruby classes and objects

Ruby is an object-oriented programming language that has classes and objects. What’s the difference?

In a nutshell:

A class is a template from which objects are built.
An object is an instance of a class.

Classes are used to create objects. Objects can be called with the methods and attributes that were defined within their class.

How to define a class

Ruby classes are defined with the class keyword and an end. The first letter of the name of the class is capitalized. All of the class’s methods and attributes are defined in between.

class Team

  def initialize(name)
	  @name = name
	end
	
	def go_team
	  "Let's go, #{@name}!"
	end

end

In the above example, an instance (or object) of the Team class is given a name when it’s initialized, or first made:

philly = Team.new("Eagles)"

In the code above, the philly variable is equal to a new instance of Team with the name of "Eagles". (Note that any value can be used for the variable, but it makes sense to use a variable that corresponds with the object that you’re creating.) You can then call:

philly.go_team

The return value would be:

"Let's go, Eagles!"

To create another object, or instance, of Team to represent another team:

cleveland = Team.new("Browns")

And to cheer on that team, you can run:

cleveland.go_team

To get a return value of:

"Let's go, Browns!"

To reiterate: In the above example, Team is the class. philly and cleveland are equal to two difference instances, or objects, of that class.

Another example

The Car class has two attributes, make and model, and two methods: vroom, which returns "Off we go!", and sweet_ride, which returns a string using the object’s make and model:

class Car

  def initialize(make, model)
	  @make = make
		@model = model
	end
	
	def vroom
	  "Off we go!"
	end
	
	def sweet_ride
	  "I really like your ${@make} ${@model}!"
	end
	
end

Let’s see it in action:

civic = Car.new("Honda", "Civic")

civic.vroom
 => "Off we go!" 
 
civic.sweet_ride
 => "I really like your Honda Civic!" 
 
mustang = Car.new("Ford", "Mustang")

mustang.sweet_ride
 => "I really like your Ford Mustang!" 

mustang.vroom
 => "Off we go!" 

Car is the class. civic and mustang are objects, or instances, of the class.