当调用instance_eval（＆lambda）来传递当前上下文时得到错误'错误的参数个数'

To be clear - this code is running perfectly - code with proc

要清楚 - 这段代码运行完美 - 带proc的代码

but if instead I change Proc.new to lambda, I'm getting an error

但如果相反我将Proc.new更改为lambda,我收到错误

ArgumentError: wrong number of arguments (1 for 0)

May be this is because instance_eval wants to pass self as a param, and lambda treats as a method and do not accept unknown params?

可能这是因为instance_eval想要将self作为一个参数传递,而lambda视为一种方法并且不接受未知的params?

There is two examples - first is working:

有两个例子 - 首先是工作:

class Rule
  def get_rule
    Proc.new { puts name }
  end
end

class Person
  attr_accessor :name

  def init_rule 
    @name = "ruby"
    instance_eval(&Rule.new.get_rule)
  end
end

second is not:

第二个不是:

class Rule
  def get_rule
    lambda { puts name }
  end
end

class Person
   attr_accessor :name

   def init_rule 
     @name = "ruby"
     instance_eval(&Rule.new.get_rule)
   end
end

Thanks

1 个解决方案

#1

You are actually correct in your assumption. Self is being passed to the Proc and to the lambda as it is being instance_eval'ed. A major difference between Procs and lambdas is that lambdas check the arity of the block being being passed to them.

你的假设实际上是正确的。 Self正被传递给Proc和lambda,因为它是instance_eval。 Procs和lambdas之间的一个主要区别是lambdas检查正在传递给它们的块的arity。

So:

 class Rule
   def get_rule
     lambda { |s| puts s.inspect; puts name; }
   end
 end

 p = Person.new
 p.get_rule

 #<Person:0x007fd1099f53d0 @name="ruby">
 ruby 

Here I told the lambda to expect a block with arity 1 and as you see in the argument inspection, the argument is indeed the self instance of Person class.

在这里,我告诉lambda期望一个带有arity 1的块,正如你在参数检查中看到的那样,该参数确实是Person类的自我实例。