3

有什么方法可以在被调用的块中获取被调用的对象。例如，块是否有任何方法可以访问方法batman或类的范围SuperHeros

class SuperHeros

  attr_accessor :news

  def initialize
    @news = []
  end

  def batman task
    puts "Batman: #{task} - done"
    yield "feed cat"
    @news << task
  end

end

cat_woman = lambda do |task| 
  puts "Cat Woman: #{task} - done" 
  # invoker.news << task
end

robin = lambda do |task| 
  puts "Robin: #{task} - done"
  # invoker.news << task
end


characters = SuperHeros.new
characters.batman("kick Joker's ass", &cat_woman)
characters.batman("break Bane's bones", &robin)
4

2 回答 2

2

您可以使用类似于Instance eval 和委托模式的东西，例如在Savon gem 中使用：

def batman(task, &block)
  @original_self = eval('self', block.binding)
  puts "Batman: #{task} - done"
  instance_exec('feed cat', &block)
  @news << task
end

private

def method_missing(method, *args, &block)
  if @original_self
    @original_self.send(method, *args, &block)
  else
    super
  end
end

在这种方法中，当您在传递给方法的块内调用方法（使用隐式接收器）时，它会在实例batman的上下文中调用。SuperHeros如果没有可用的此类方法，则调用（通过method_missing）到原始块self。

于 2013-11-07T11:10:23.047 回答
0

在块中获取接收器对象的最简单方法是将对象分配给实例变量。

这个例子更清楚地说明了 lambdas cat_woman 和 robin 如何访问块的接收者对象的属性：

class SuperHeros
  attr_accessor :news, :name, :current_task

  def initialize(a_name)
    @name = a_name
    @news = []
  end

  def batman(task)
    puts "Inside the method batman of #{name}: #{task} in progress ..."
    @current_task = task
    yield
    @news << task
  end

end

cat_woman = lambda do |extra_task|
  puts "cat_woman even #{extra_task} before doing #{@caller_obj.current_task}"
  puts "Cat Woman: #{@caller_obj.current_task} - done by #{@caller_obj.name}"
  # invoker.news << task
end

robin = lambda do |extra_task|
  puts "robin even #{extra_task} before doing #{@caller_obj.current_task}"
  puts "Robin: #{@caller_obj.current_task} - done by #{@caller_obj.name}"
end


character_1 = SuperHeros.new('batman_1')
(@caller_obj = character_1).batman("kick Joker's ass") { cat_woman['eats some burger'] }

puts

character_2 = SuperHeros.new('batman_2')
(@caller_obj = character_2).batman("break Bane's bones") { robin['drinks some beer'] }

输出将是：

Inside the method batman of batman_1: kick Joker's ass in progress ...
cat_woman even eats some burger before doing kick Joker's ass
Cat Woman: kick Joker's ass - done by batman_1

Inside the method batman of batman_2: break Bane's bones in progress ...
robin even drinks some beer before doing break Bane's bones
Robin: break Bane's bones - done by batman_2
于 2017-02-17T00:50:54.090 回答