Ruby: initialize() vs class body?

Question

In Ruby, what is the difference between putting code in an initialize() method rather than directly in the class body? Both appear to be executed when calling MyClass.new.

Clearly, initialize() can accept parameters, but is that the only difference?

class MyClass   puts 'Hello'    def initialize(params)     puts 'World'   end end 

Answer 1

Try to create two instances of MyClass

a = MyClass.new b = MyClass.new 

to see the difference:

Hello

World

World

Code in the class body execute only once - when ruby loads the file. initialize() executes every time you create a new instance of your class.

Answer 2

Well, initialize gets called by new, whereas the class body gets evaluated on class definition/loading.

Additionally, try setting an instance variable in the class body or in initialize. You'll notice the latter will belong to the created object, whereas the first will belong to the class instance (hence the name class instance variable).