Tuesday, April 24, 2007

Ruby is Object Oriented

Answering to requests of our hundreds of readers :) I'm going to continue posting about Ruby language. So, today I'm going to say about object orientation in Ruby, specifically how to write a simple class, write methods (that's what I know to do with Ruby for the time being), etc.

So, below you can see a simple class written in Ruby:

class MyClass

And an object instantiation:
m = MyClass.new

Adding methods is very easy too:

class MyClass
def my_method
puts "That's a Ruby method!";

If you're using irb (interactive ruby), a tool to execute interactively ruby expressions read from stdin, you don't have to re-instantiate 'm', the changes made in MyClass will affect 'm' dynamically (on the fly), so if you call 'm.my_method', don't worry, it'll work.

If you're not sure about a method in a object, you can do this:

if m.respond_to? "my_method"

Do I need to explain something else?

The 'initialize' method represents a constructor in a Ruby class and the parameters come after:

class MyClass
def initialize name = "Hello World!"
@name = name
def hello
puts "#{@name}"

The '@name' is a field, like 'private Object obj;' in Java, and in the case above 'name' has "Hello World!" as its default value.

If you try to call 'm.name' you'll get something like:

NoMethodError: undefined method `name' for ...

This is because name is 'private', to create 'getters' and 'setters' you have to add 'attr_accessor :name' before the constructor. So, after that you can call 'm.name' or 'm.name = "hello"', for example, as you wish.

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