do_ruby.rb

class Foo
  def foo(arg=nil)
    p arg
  end
end

class Bar < Foo
  def foo(arg)
    # 5を引数にして呼び出す
    super(5)                    # => 5
    # 5を引数にして呼び出す
    super(arg)                  # => 5
    # 5を引数にして呼び出す super(arg)の略記法
    super                       # => 5
    arg = 1
    # 1を引数にして呼び出す super(arg)の略記法
    super                       # => 1
    # 引数なしで呼び出す
    super()                     # => nil
  end
end

Bar.new.foo 5                   # => nil

class Sample
  @value = 'hello'
  def value
    @value # !> instance variable @value not initialized
  end
end

Sample.new.value                # => nil
Sample.class_eval { @value }    # => "hello"
#
class Foo
  @v1 = 1

  def self.read
    @v1
  end

  def write
    @v1 = 2
  end

  def read
    @v1
  end
end

obj = Foo.new
obj.write                       # => 2
obj.read                        # => 2
Foo.read                        # => 1
#
foo = Foo.new
foo.class                       # => Foo
# foo.superclass                  # => 
@@v1 = 1 # !> class variable access from toplevel
class Foo
  @@v1 = 2
end
p @@v1 # 2 # !> class variable access from toplevel
# クラス変数は親と子、共有で使う

# http://ref.xaio.jp/ruby/classes/object/extend
module M
  def m
    'aa'
  end
end

obj = Object.new
obj.extend M
obj.m                           # => "aa"

class C
  extend M
end

C.m                             # => "aa"

#c.new.m                         # =>

# includeの位置を変えると表示される結果が異なる
module M
  @@x = 100
end

class A
  @@x = 500
  include M
end

module M
  p @@x                         # => 100
end

module AB
  p @@x                         # => 
end


# ~> -:100:in `<module:AB>': uninitialized class variable @@x in AB (NameError)
# ~> 	from -:99:in `<main>'
# >> 5
# >> 5
# >> 5
# >> 1
# >> nil
# >> 2
# >> 100