Ruby 类变量

Question

ruby 类实例的东西让我很头疼。我明白了……

class Foo
  @var = 'bar'
end

...@var 是已创建类实例上的一个变量。

但是如何创建一个子类可重写的类变量呢？

这是我将在 Python 中执行的操作的示例:

class Fish:
var = 'fish'
def v(self):
    return self.var

class Trout(Fish):
    var = 'trout'

class Salmon(Fish):
    var = 'salmon'

print Trout().v()
print Salmon().v()

哪些输出:

trout
salmon

我如何在 ruby​​ 中做同样的事情？

Answer 1

为了对比@khelll 的回答，这在 Class 对象上使用了实例变量:

class Fish
  # an instance variable of this Class object
  @var = 'fish'

  # the "getter"
  def self.v
    @var
  end

  # the "setter"
  def self.v=(a_fish)
    @var = a_fish
  end
end

class Trout < Fish
  self.v = 'trout'
end

class Salmon < Fish
  self.v = 'salmon'
end

p Trout.v   # => "trout"
p Salmon.v  # => "salmon"

编辑:赋予实例对类的实例变量的读取权限:

class Fish
  def type_of_fish
    self.class.v
  end
end

p Trout.new.type_of_fish   # => "trout"
p Salmon.new.type_of_fish  # => "salmon"