何时使用lambda，何时使用Proc.new? [英] When to use lambda, when to use Proc.new?

问题描述

在Ruby 1.8中，一方面proc/lambda和另一方面Proc.new之间存在细微的差异.

In Ruby 1.8, there are subtle differences between proc/lambda on the one hand, and Proc.new on the other.

• 这些区别是什么?
• 您能提供有关如何决定选择哪一个的指南吗?
• 在Ruby 1.9中，proc和lambda是不同的.怎么了?

推荐答案

使用lambda创建的proc和使用Proc.new创建的proc之间的另一个重要但细微的区别是它们如何处理return语句:

Another important but subtle difference between procs created with lambda and procs created with Proc.new is how they handle the return statement:

• 在lambda创建的proc中，return语句仅从proc本身返回
• 在Proc.new创建的proc中，return语句有点令人惊讶:它不仅从proc，而且还从封装proc的方法中返回控制！

• In a lambda-created proc, the return statement returns only from the proc itself
• In a Proc.new-created proc, the return statement is a little more surprising: it returns control not just from the proc, but also from the method enclosing the proc!

这里是lambda创建的proc的return的作用.它的行为可能与您预期的一样:

Here's lambda-created proc's return in action. It behaves in a way that you probably expect:

def whowouldwin

  mylambda = lambda {return "Freddy"}
  mylambda.call

  # mylambda gets called and returns "Freddy", and execution
  # continues on the next line

  return "Jason"

end


whowouldwin
#=> "Jason"

现在这是一个Proc.new创建的proc的return在做同样的事情.您将看到以下其中一种情况，其中Ruby打破了广受赞誉的最小惊喜原则":

Now here's a Proc.new-created proc's return doing the same thing. You're about to see one of those cases where Ruby breaks the much-vaunted Principle of Least Surprise:

def whowouldwin2

  myproc = Proc.new {return "Freddy"}
  myproc.call

  # myproc gets called and returns "Freddy", 
  # but also returns control from whowhouldwin2!
  # The line below *never* gets executed.

  return "Jason"

end


whowouldwin2         
#=> "Freddy"

由于这种令人惊讶的行为(以及更少的键入)，在制作proc时，我倾向于使用lambda而不是Proc.new.

Thanks to this surprising behavior (as well as less typing), I tend to favor using lambda over Proc.new when making procs.

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