Rubyのインスタンス変数・メソッドとクラス変数・メソッドを検証 ref: http://qiita.com/hiroykam/items/9b47ca3fc05afbf91903

file0.txt

class Test
  @c_i_var = 0
  @@c_var = 10
  var = 'var'

  def initialize
    @i_var = 100
  end

  def test
    @i_var   += 1
    @@c_var   += 1
    self
  end

  def examine1
    p 'Test::examine1'
    p @i_var, @c_i_var, @@c_var
    self
  end

  def Test.examine2
    @c_i_var += 1
    p 'Test::examine2'
    p @i_var, @c_i_var, @@c_var
    Test.new
  end

  def examine3
    Test
  end

  p 'Test::var'
  p var
end

class Test2 < Test
  def Test2.examine2
    p 'Test2::examine2'
    p @i_var, @c_i_var, @@c_var
  end
end

t = Test.new
t.test.examine1
Test.examine2.test.examine1.examine3.examine2

Test2.examine2

file1.txt

"Test::var"
"var"
"Test::examine1"
101
nil
11
"Test::examine2"
nil
1
11
"Test::examine1"
101
nil
12
"Test::examine2"
nil
2
12
"Test2::examine2"
nil
nil
12

file2.txt

class Test
  @@c_var = 2

  def initialize(val)
    @i_var = val
  end

  def inspect
    '%d, %d' % [@@c_var, @i_var]
  end

  def examine1
    @i_var += 2
    self
  end

  def examine2
    @@c_var += 2
    self
  end
end

t1 = Test.new(3)
t1.examine1.examine2
p t1
p Test.new(3)

puts '--- shallow copy ---'

t2 = t1.clone
t2.examine1.examine2
p t1
p t2
p Test.new(3)

puts '--- deep copy ---'

t3 = Marshal.load(Marshal.dump(t1))
t3.examine1.examine2
p t1
p t2
p t3
p Test.new(3)

file3.txt

4, 5
4, 3
--- shallow copy ---
6, 5
6, 7
6, 3
--- deep copy ---
8, 5
8, 7
8, 7
8, 3