别名方法链未定义方法

Question

出于某种原因,我的alias_method_chain不想工作,我不知道为什么.任何人都可以向我解释为什么以下不起作用？

[2] pry(main)> Client.respond_to? :mapping
=> true
[3] pry(main)> Client.alias_method_chain :mapping, :safety
NameError: undefined method `mapping' for class `Client'

Answer 1

要为某个类的对象获取别名方法链,您应该调用alias_method_chain类本身而不是它的实例.如果你想使类链方法适用相同的规则:你应该调用alias_method_chain类的单例类,可以像这样获得:

klass = class << Client; self; end  # => returns singleton class for Client class

在这种情况下Client是一个klass类的实例(以Class类作为其超类).

类方法链的结果示例如下:

class Client
  def self.mapping
    puts 'mapping'
  end

  def self.mapping_with_safety
    puts 'safety'
    mapping_without_safety
  end

  class << self
    # call alias_method_chain in context of Client's singleton class
    alias_method_chain :mapping, :safety
  end
end

# alternatively you can do it outside of Client class like that 
# (class << Client; self; end).alias_method_chain :mapping, :safety

Client.mapping
# => safety
# => mapping