如何动态定义ruby中的实例方法？

Question

I want to dynamically create instance method of child class through class method of parent class.

class Foo
  def self.add_fizz_method &body
    # ??? (This is line 3)
  end
end

class Bar < Foo
end
Bar.new.fizz #=> nil

class Bar
  add_fizz_method do
    p "i like turtles"
  end
end
Bar.new.fizz #=> "i like turtles"

What to write on line #3?

Answer 1

use define_method like this:

class Foo
  def self.add_fizz_method &block
    define_method 'fizz', &block
  end
end

class Bar < Foo; end

begin
  Bar.new.fizz 
rescue NoMethodError
  puts 'method undefined'
end

Bar.add_fizz_method do
  p 'i like turtles'
end
Bar.new.fizz

output:

method undefined
"i like turtles"

Answer 2

define_method 'fizz' do
  puts 'fizz'
end

...or accepting a block

define_method 'fizz', &block