Ruby Class Methods vs. Methods in Eigenclasses

Question

Are class methods and methods in the eigenclass (or metaclass) of that class just two ways to define one thing?

Otherwise, what are the differences?

cla         


        

Answer 1

The two methods are equivalent. The 'eigenclass' version is helpful for using the attr_* methods, for example:

class Foo
  @instances = []
  class << self;
    attr_reader :instances
  end
  def initialize
    self.class.instances << self
  end
end

2.times{ Foo.new }
p Foo.instances
#=> [#, #]

You can also use define_singleton_method to create methods on the class:

Foo.define_singleton_method :bim do "bam!" end