ruby - Ruby 中类变量的 Getter/Setter

Question

是否可以为类变量自动生成/启用 getter/setter，就像使用 attr_accessor 为实例变量生成的那样:

class School
  @@syllabus = :cbse

  def self.syllabus
    @@syllabus
  end

  def self.syllabus=(_)
    @@syllabus = _
  end
end

School.syllabus = :icse
School.syllabus # => :icse

Answer 1

您需要做的就是在类的范围内声明attr_accessor:

class School
 class << self
   attr_accessor :syllabus
  end
end

School.syllabus = :icse
School.syllabus # => :icse

请注意，底层成员不会是@@syllabus(没有针对此类变量的内置解决方案)而是@syllabus 在类范围内，无论如何这是推荐的方法，参见 this关于两者区别的博文:

The issue with class variables is inheritance. Let’s say I want to subclass Polygon with Triangle like so:

class Triangle < Polygon
  @@sides = 3
end

puts Triangle.sides # => 3
puts Polygon.sides # => 3

Wha? But Polygon’s sides was set to 10? When you set a class variable, you set it for the superclass and all of the subclasses.