Classes and objects

Define a class

A class is a blueprint for objects. It groups data and behavior in one named place, so related methods live next to the values they use.

Shared behavior can also come from outside the class, as shown in Modules and mixins.

class User def hello puts "Hello" end end user = User.new user.hello

Initialize objects

When you call new, Ruby builds a fresh object and runs a special method named initialize. It receives the arguments you pass to new and stores them in instance variables that start with @.

Each object keeps its own copy of these variables, so two users never share a name.

class User def initialize(name) @name = name end def hello puts "Hello, " + @name end end user = User.new("Ada") user.hello

attr_reader and accessor

Instance variables hide inside the object. To read them from outside, declare attr_reader with the variable name without @.

Use attr_accessor when outside code must also change the value. Prefer the reader by default and open writing only where needed.

class User attr_reader :name attr_accessor :email def initialize(name) @name = name end end user = User.new("Ada") puts user.name

What self is

Inside a method, self is the current object, the one that received the call. You can call other methods on it or print it for inspection.

At the top level of a program self is a plain object called main, which is why small scripts can call methods without a receiver.

class Counter def show_self puts self end end Counter.new.show_self

Next: Inheritance

Article author: Arthur Isaev