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锁定老帖子 主题：Closure & Block
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发表时间：2006-11-15
问题：Block & closure的分别是什么，差别是什么，分别适应什么样的情况！
在我概念中一直觉得Ruby的Block和C/C++中的函数指针是类似，只是他写法更简单。对于Python和lisp来说function是一等公民，所以也可以实现和Ruby的Block一样的功能。其实对于Java程序员来说，我认为Block更像匿名内部类。今天找到一篇权威的文章http://www.artima.com/intv/closures.html。 该文中提到Closure可以和Block互相转换，而他们的差别就是Closure具有context。不是很理解Closure的含义。目前也暂时想不到什么情况下使用Closure强于使用Block,希望大家share一下。 引用 Bill Venners: Ruby supports blocks and closures. What are blocks and closures, and how are they used? Yukihiro Matsumoto: Blocks are basically nameless functions. You may be familiar with the lambda from other languages like Lisp or Python. Basically, you can pass a nameless function to another function, and then that function can invoke the passed-in nameless function. For example, a function could perform iteration by passing one item at a time to the nameless function. This is a common style, called higher order function style, among languages that can handle functions as first class objects. Lisp does it. Python does it .Even C does it with function pointers. Many other languages do this style of programming. In Ruby, the difference is mainly a different kind of syntax for higher order functions. In other languages, you have to specify explicitly that a function can accept another function as an argument. But in Ruby, any method can be called with a block as an implicit argument. Inside the method, you can call the block using the yield keyword with a value. 声明：ITeye文章版权属于作者，受法律保护。没有作者书面许可不得转载。
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发表时间：2006-11-15
geradle 写道 该文中提到Closure可以和Block互相转换，而他们的差别就是Closure具有context。不是很理解Closure的含义。目前也暂时想不到什么情况下使用Closure强于使用Block,希望大家share一下。 这个解释是正确的。前几天在编写xruby的builtin时发现编译器的一个bug，把block当成closure来实现了，结果block中的return没有跳出函数作用域，比如下面这段代码：
def test
3.times do
return
end
end
在block中，这个return是直接跳出函数的，当时是结束当前循环，所以最终的结果是3次循环都执行了，函数也执行到最后。 |
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发表时间：2006-11-15
按照SICP的说法，Closure有两个含义，第一个指的就是离散数学中的定义，大概意思是：
一个定义域和函数集合，使得函数的值域仍然落进定义域。 后来不知道为什么这个词用来形容包含自由变量的函数,这个自由变量就是上面所说的Context。 其实这两个定义没有任何关系。 |
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发表时间：2006-11-15
唉，Ruby的Closure,Proc,Block这三个概念太相似了，难于区别，虽然不理解也可以写代码，但是还是理解的好。
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发表时间：2006-11-16
Here is a MF article about closure
www.martinfowler.com/bliki/Closure.html |
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发表时间：2006-11-16
roseanne 写道 Here is a MF article about closure
www.martinfowler.com/bliki/Closure.html roseanne为什么老用英文写呀？计算机输入不了中文么？ 
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发表时间：2006-11-16
roseanne 写道 Here is a MF article about closure
www.martinfowler.com/bliki/Closure.html 这个文章没有讲三者的差别，只是讲了Closure的作用，Closure的作用我已经理解，其在Python中也有对应的实现。 我现在的疑问是，Ruby中这三个东西到底有什么细微的差别，说实话我觉得有点重复了。所以有点疑惑！ |
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发表时间：2006-11-17
qiezi was correct.
I read and tested a lot, finally understand the similarity and difference now. Put together an example code, try to run it, you would understand too. The key is return!
def test_closure_or_not(closure_or_not)
puts
puts "before calling closure_or_not"
result = closure_or_not.call
puts "after calling closure_or_not"
puts "result from closure_or_not: #{result}"
"test_closure_or_not result"
end
def test_block(&b)
puts
puts "before calling block"
result = b.call
puts "after calling block"
puts "result from block: #{result}"
"test_block result"
end
puts "======w/o return======"
# all three are fine without return
puts "w/o return:" + test_closure_or_not(lambda {"from lambda"})
puts "w/o return:" + test_closure_or_not(Proc.new {"from Proc.new"})
puts "w/o return:" + test_block{"from block"}
puts "======w/ return======"
# Only lambda is fine with return,
# lambda is closure, block and Proc.new are not
puts "w/ return:" + test_closure_or_not(lambda {return "from lambda"})
puts "w/ return:" + test_closure_or_not(Proc.new {return "from Proc.new"})
puts "w/ return:" + test_block{return "from block"}
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发表时间：2006-11-17
Pay attention to the comments in code.
Thanks! |
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发表时间：2006-11-17
Thanks roseanne. Now, I know the key is return, but I want to ask why?
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