ruby 动态添加类变量

Question

例子:

class Base
  @@var = "base"

  def self.assign_var(var)
    @@var = var
  end

  def self.show_var
    @@var
  end

  def initialize
    p @@var
  end

end

class A < Base
  assign_var("a")
end

class B < Base
  assign_var("b")
end

class C < Base
  assign_var("c")
end

p A.show_var # "c"
p B.show_var # "c"
p C.show_var # "c"
a = A.new # "c"
b = B.new # "c"
c = C.new # "c"

如何让他们在类(class)中展现自己的值(value)分配？像这样:

p A.show_var # "a"
p B.show_var # "b"
p C.show_var # "c"
a = A.new # "a"
b = B.new # "b"
c = C.new # "c"

---

更新

我需要在初始化程序中访问这个变量。

class Base
  @var = "base"

  def self.assign_var(var)
    @var = var
  end

  def self.show_var
    @var
  end

  def initialize
    p @var
  end
end

class A < Base
  assign_var("a")
end

class B < Base
  assign_var("b")
end

class C < Base
  assign_var("c")
end

p A.show_var # "a"
p B.show_var # "b"
p C.show_var # "c"
a = A.new # nil
b = B.new # nil
c = C.new # nil

如果我使用 Vu 的解决方案，它不起作用...有什么想法吗？

Answer 1

类变量没有在子类中重新定义。在这种情况下，您可以使用类级实例变量:

class Base
  @var = "base"

  def self.assign_var(var)
    @var = var
  end

  def self.show_var
    @var
  end
end

class A < Base
  assign_var("a")
end

class B < Base
  assign_var("b")
end

class C < Base
  assign_var("c")
end

p A.show_var # "a"
p B.show_var # "b"
p C.show_var # "c"

更多信息: http://www.railstips.org/blog/archives/2006/11/18/class-and-instance-variables-in-ruby/