Classes, Objects, and Variables

June 18 2015

"Ruby is a perfect Object Oriented Programming Language. Everyting in Ruby is object."

Object orientention is not only development style. If you look around you'll see objects are everywhere: your car, your dog. And every objects has state and behavior. Take for example dog: state(name, color, breed) and behavior (barking, fetching). So for every objects which you see ask yoursefl two questoins: "What possible states can this object be in?" and "What possible behavior can this object perform?".

Let's start from example. We created class Square

What we did in this example

The class keyword define a class.
The initialize method is what actually constructs the data structure. Every class must contain an initialize method.
@side_length is an object variable. Similar to the keys of a hash. The @ sign distinguishes @street as an object variable. Every time you create an object of the class Square, this object will contain a @side_length variable.

Let's create a new instance of class Square.

Getter and Setter methods

Ok. Now we have class Square and already created instance of this class. But what if you want now read or rewrite side_length. How we can do this. For this purpose we need getter and setter method.

But making our code more elegant we can use attr_reader and attr_writer in Ruby.
attr_reader is a getter which means that it just returns a value or state outside of the class, but does not change it.
attr_writer is a setter which means that you can change the value of the variable outside of the class, but it is not readable.

Methods

Inside our class Square we already have method initialize. Now we will add method area and method perimetr

All of this methods are objects methods.