attr_accessor与attr_reader和实例变量

Question

谁能告诉我两者之间的区别(如果有的话)

class Car
  attr_accessor :engine
  def initialize(engine)
    self.engine = engine
  end
end

和

class Car
  attr_reader :engine
  def initialize(engine)
    @engine = engine
  end
end

或者它们几乎相同？

Answer 1

attr_accessor定义getter和setter.attr_reader仅定义getter.

class Car
  attr_reader :engine
  def initialize(engine)
    @engine = engine
  end
end

Car.instance_methods(false) # => [:engine]

使用上面的代码,您只能定义def engine; @engine ;end.

class Car
  attr_accessor :engine
  def initialize(engine)
    self.engine = engine
  end
end

Car.instance_methods(false) # => [:engine, :engine=]

使用上面的代码,您只定义def engine; @engine ;end和def engine=(engine) ;@engine = engine ;end.

Answer 2

attr_accessor :engine允许您读取和写入变量@engine。

attr_reader :engine只允许你读取@engine 的值

self.engine = engine和@engine = engine几乎做同样的事情。