12 - undefining a method.rb

O Reilly Ruby Cookbook source code

class RandomizingArray < Array
  def <<(e)
    insert(rand(size), e)   
  end
  
  def [](i)
    super(rand(size))
  end
end

a = RandomizingArray.new
a << 1 << 2 << 3 << 4 << 5 << 6           # => [6, 3, 4, 5, 2, 1]

# That was fun; now let's get some of those entries back.
a[0]                                      # => 1
a[0]                                      # => 2
a[0]                                      # => 5
#No, seriously, a[0].
a[0]                                      # => 4
#It's a madhouse! A madhouse!
a[0]                                      # => 3
#That does it!

class RandomizingArray
  remove_method('[]')
end

a[0]                                      # => 6
a[0]                                      # => 6
a[0]                                      # => 6

# But the overridden << operator still works randomly:
a << 7                                    # => [6, 3, 4, 7, 5, 2, 1]
#---
class RandomizingArray
  remove_method(:length)
end
# NameError: method `length' not defined in RandomizingArray

class RandomizingArray
  undef_method(:length)
end

RandomizingArray.new.length                
# NoMethodError: undefined method `length' for []:RandomizingArray
Array.new.length                                   # => 0
#---
my_array = Array.new
def my_array.random_dump(number)
  number.times { self << rand(100) }
end

my_array.random_dump(3)
my_array.random_dump(2)
my_array                                      # => [6, 45, 12, 49, 66]

# That's enough of that.
class << my_array
  remove_method(:random_dump)
end
my_array.random_dump(4)
# NoMethodError: undefined method `random_dump' for [6, 45, 12, 49, 66]:Array
#---
class OneTimeContainer
  def initialize(value)
    @use_just_once_then_destroy = value
  end

  def get_value
    remove_instance_variable(:@use_just_once_then_destroy)    
  end
end

object_1 = OneTimeContainer.new(6)
object_1.get_value
# => 6
object_1.get_value
# NameError: instance variable @use_just_once_then_destroy not defined

object_2 = OneTimeContainer.new('ephemeron')
object_2.get_value
# => "ephemeron"
#---
class MyClass
  remove_instance_variable(:@use_just_once_then_destroy)    
end
# NameError: instance variable @use_just_once_then_destroy not defined
#---