问题
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When to use lambda, when to use Proc.new?
(I know it had been asked several times but I couldn't find satisfactory answer)Can somebody please explain Blocks, Procs and Lambdas and why one should be used over other, what are the situation when one should use proc, similar and/or lambda. Also there effect on computer memory. Practical examples please.
回答1:
Try Robert Sosinski's Tutorial or Learning to Program by Chris Pine.
For more foundation I suggest you read Why’s (poignant) Guide to Ruby. This guide is responsible for creating many of nowadays Ruby's Pro! Make sure to take a look!
Explanation by Joey deVilla
Another important but subtle difference is in the way procs created with lambda
and procs created with Proc.new
handle the return
statement:
- In a
lambda
-created proc, thereturn
statement returns only from the proc itself - In a
Proc.new
-created proc, thereturn
statement is a little more surprising: it returns control not just from the proc, but also from the method enclosing the proc!
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"
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"
Thanks to this surprising behaviour (as well as less typing), I tend to favour using lambda
over Proc.new
when making procs.
来源:https://stackoverflow.com/questions/11581308/what-are-procs-and-lambdas-practical-examples-please