Ruby/Reflection/method missing

class CommandWrapper
  def method_missing(method, *args)
    system(method.to_s, *args)
  end
end
 
cw = CommandWrapper.new
cw.date                   # Sat Apr 28 22:50:11 CDT 2001
cw.du "-s", "/tmp"        # 166749  /tmp

class BackwardsString
  def initialize(s)
   @s = s
  end
  def method_missing(m, *args, &block)
    result = @s.send(m, *args, &block)
    result.respond_to?(:to_str) ? BackwardsString.new(result) : result
  end
  def to_s
    @s.reverse
  end
  def inspect
    to_s
  end
end
s = BackwardsString.new("I"m backwards.")             # => .sdrawkcab m"I
s.size                                                # => 14
s.upcase                                              # => .SDRAWKCAB M"I
s.reverse                                             # => I"m backwards.
s.no_such_method
# NoMethodError: undefined method "no_such_method" for "I"m backwards.":String

class StringFactory
  def StringFactory.method_missing(m, *args)
    return String.new(m.to_s, *args)
  end
end
puts StringFactory.a_string                      # => "a_string"
puts StringFactory.another_string                # => "another_string"

class Library  < Array
  def add_book(author, title)
    self << [author, title]
  end
  def search_by_author(key)
    reject { |b| !match(b, 0, key) }
  end
  def search_by_author_or_title(key)
    reject { |b| !match(b, 0, key) && !match(b, 1, key) }
  end
  :private
  def match(b, index, key)
    b[index].index(key) != nil
  end
  def method_missing(m, *args)
    search_by_author_or_title(m.to_s)
  end
end
l = Library.new("author","title")
p l.a
p l.b
p l.c

class Fixnum
  def method_missing(m, *args)
    if args.size > 0
      raise ArgumentError.new("wrong number of arguments (#{args.size} for 0)")
    end
    match = /^plus_([0-9]+)$/.match(m.to_s)
    if match
      self + match.captures[0].to_i
    else
      raise NoMethodError.
    new("undefined method "#{m}" for #{inspect}:#{self.class}")
    end
  end
end
4.plus_5                                          # => 9
10.plus_0                                         # => 10
-1.plus_2                                         # => 1
100.plus_10000                                    # => 10100
20.send(:plus_25)                                 # => 45
100.minus_3
# NoMethodError: undefined method "minus_3" for 100:Fixnum
100.plus_5(105)
# ArgumentError: wrong number of arguments (1 for 0)

class MyClass
  def defined_method
    "This method is defined."
  end
  def method_missing(m, *args)
    "Sorry, I don"t know about any #{m} method."
  end
end
o = MyClass.new
o.defined_method                         # => "This method is defined."
o.undefined_method
# => "Sorry, I don"t know about any undefined_method method."