我可以在Ruby中通过字符串引用对象的属性吗？

Question

If I have a ruby class called Node:

class Node
  attr_accessor :a, :b, :c
  attr_reader :key
  def initialize(key)
    @key = key
  end
  def [](letter)
    if letter == 'a'
      return self.a
    elsif letter == 'b'
      return self.b
    elsif letter == 'c'
      return self.c
    end
  end
end

How can I optimize def [](letter) so I won't have repetitive code? More specifically, how can I access an attribute of an object (that is a ruby symbol :a , :b , or :c ) by using a corresponding string?

Answer 1

You can use send , which invokes a method dynamically on the caller, in this case self :

class Node
  def [](key)
    key = key.to_sym
    send(key) if respond_to?(key)
  end
end

Note that we check that self has the appropriate method before calling it. This avoids getting a NoMethodError and instead results in node_instance[:banana] returning nil , which is appropriate given the interface.

By the way, if this is the majority of the behavior of your Node class, you may simply want to use an OpenStruct:

require 'ostruct'
node_instance = OpenStruct.new(a: 'Apple', b: 'Banana')
node_instance.a    #=> 'Apple'
node_instance['b'] #=> 'Banana'
node_instance.c = 'Chocolate'
node_instance[:c]  #=> 'Chocolate'