Ruby:使用instance\u eval(&lambda)和instance\u eval{lambda.呼叫}

我想叫一个lambda改变它的自我价值。为了寻找它,我来到了 instance_exec ,本该完成任务的。

然而,经过1个多小时的学习,我发现这个行为我无法解释:

class Dummy

  class << self

    attr_accessor :my_lambda

  end

  self.my_lambda = proc { self }

  def test
    self.class.my_lambda.call
  end

  def test1
    instance_eval(&self.class.my_lambda)
  end

  def test2
    instance_eval { self.class.my_lambda.call }
  end

end

Dummy.new.test
=> Dummy # I was expecting this, returns the class, lexical scope (where `self` was defined)

Dummy.new.test1
=> #<Dummy:0x00007fe982f8b678> # I was expecting this, `self` changed to the receiver of `instance_eval`, which is the instance, so `self` returned the instance.

Dummy.new.test2
=> Dummy # I can't understand this, at all. Why isn't it the same as test1?

那么,为什么我们从中得到不同的结果呢 instance_eval(&self.class.my_lambda) 与 instance_eval { self.class.my_lambda.call } ?

另外,既然我们现在的主题是叫Lambdas。。。如果我将类级别变量更改为:

self.my_lambda = lambda { self }

那么虚拟新试验1引发异常 ArgumentError: wrong number of arguments (given 1, expected 0) 实例评估(&U);自我类我的lambda)