class Class - instance vs. class methods

Question

How is it that this works? When the following is run "hi from class" is printed twice. What is going on inside ruby to make this behave like this? Am I NOT in fact making an instance method for class

class Class
  def foo
    puts "hi from class" 
  end
end

Class.foo
x = Class.new
x.foo

sepp2k · Accepted Answer · 2011-10-03 18:28:02Z

9

I don't know whether you're aware of that, but when you do class Class ... end, you're not creating a new class named Class, you're reopening the existing class Class.

Since Class is the class that all classes are instances of that means that Class is an instance of itself. And because of that you can call any instance methods of Class directly on Class the same way you can on any other class.

answered Oct 3, 2011 at 18:28

sepp2k

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2 Comments

slindsey3000 Over a year ago

So what happens when (in the body of class Class) I def self.foo; puts "hi from **self**"; end; ... now the statement Class.foo prints hi from self?

sepp2k Over a year ago

@slindsey3000: If you define both an instance method and a class method on Class then Class.foo will call the class method and AnyOtherClass.foo will call the instance method. So in your example Class.foo will print hi from **self** and e.g. String.foo will print hi from class.

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