什麼是遺傳

方法是繼承的

class A
  def boo; p 'boo' end
end

class B < A; end

b = B.new
b.boo # => 'boo'

類方法是繼承的

class A
  def self.boo; p 'boo' end
end

class B < A; end

p B.boo # => 'boo'

常量是繼承的

class A
  WOO = 1
end

class B < A; end

p B::WOO # => 1

但要注意，它們可以被覆蓋：

class B
  WOO = WOO + 1
end

p B::WOO # => 2

例項變數是繼承的：

class A
  attr_accessor :ho
  def initialize
    @ho = 'haha'
  end
end

class B < A; end

b = B.new
p b.ho # => 'haha'

請注意，如果你覆蓋初始化例項變數而不呼叫 super 的方法，它們將為零。從上面繼續：

class C < A
  def initialize; end
 end

c = C.new
p c.ho    # => nil

類例項變數不會被繼承：

class A
    @foo = 'foo'
    class << self
        attr_accessor :foo
    end
end

class B < A; end

p B.foo # => nil

# The accessor is inherited, since it is a class method
#
B.foo = 'fob' # possible

類變數並不是真正繼承的

它們在基類和所有子類之間共享為 1 個變數：

class A
    @@foo = 0
    def initialize
        @@foo  += 1 
        p @@foo
    end
end

class B < A;end

a = A.new # => 1
b = B.new # => 2

從上面繼續：

class C < A
  def initialize
    @@foo = -10
    p @@foo
  end
end

a = C.new # => -10
b = B.new # => -9