ruby的blocks和closure特性明顯有別于其它的語言，其closure本身是real closure，所綁定的context是共享的而非copy，其設(shè)計(jì)思路和lisp的相同；blocks本身則可以用于實(shí)現(xiàn)closure。二者的關(guān)系如下所述 （
來源）
Yukihiro Matsumoto: You can reconvert a closure back into a block, so a closure can be used anywhere a block can be used. Often, closures are used to store the status of a block into an instance variable, because once you convert a block into a closure, it is an object that can by referenced by a variable. And of course closures can be used like they are used in other languages, such as passing around the object to customize behavior of methods. If you want to pass some code to customize a method, you can of course just pass a block. But if you want to pass the same code to more than two methods -- this is a very rare case, but if you really want to do that -- you can convert the block into a closure, and pass that same closure object to multiple methods.
- 隱式傳入，內(nèi)部用yield調(diào)用
def thrice
yield
yield
yield
end
x=1
thrice {x+=2}
- &block參數(shù)傳入，內(nèi)部直接操作&block
def six_times(&block)
thrice(&block)
thrice(&block)
end
x = 4
six_times { x += 10 }
- &block傳入，保存block為變量，然后調(diào)用block.call
def save_for_later(&b)
@saved = b # Note: no ampersand! This turns a block into a closure of sorts.
end
save_for_later { puts "Hello!" }
puts "Deferred execution of a block:"
@saved.call
@saved.call
這里的saved保存為main對(duì)象的一個(gè)成員，后邊實(shí)現(xiàn)延遲調(diào)用。
@saved_proc_new = Proc.new { puts "I'm declared with Proc.new." }
@saved_proc = proc { puts "I'm declared with proc." }
@saved_proc_new.call
@saved_proc.call
@saved_lambda = lambda { puts "I'm declared with lambda." }
@saved_lambda.call
def some_method
puts "I'm declared as a method."
end
@method_as_closure = method(:some_method)
當(dāng)對(duì)應(yīng)的block里邊包含return的時(shí)候，上述7中方式有些許的不同：
- lambda/method表現(xiàn)出真正的closure行為，僅僅返回closure本身；外部調(diào)用控制流不受影響，繼續(xù)yield或者call的下一語句執(zhí)行
- 其它幾種會(huì)跳出外部調(diào)用者的控制流，即return出調(diào)用者，yield/call之后的也不會(huì)再執(zhí)行，直接跳出到最近的end外
-
arity - 參數(shù)個(gè)數(shù)校驗(yàn)
對(duì)于調(diào)用點(diǎn)的參數(shù)檢查，呈現(xiàn)如下行為：
- lambda/method嚴(yán)格校驗(yàn)參數(shù)的個(gè)數(shù)，如果不匹配回拋出異常
- 其它幾個(gè)不檢查參數(shù)個(gè)數(shù)
lambda/method方式呈現(xiàn)完備的closure行為，return之后繼續(xù)下一流程，對(duì)于實(shí)際傳入?yún)?shù)個(gè)數(shù)會(huì)在調(diào)用點(diǎn)檢查；proc/blocks方式在return的時(shí)候直接返回了外部的函數(shù)或者block，對(duì)于傳入的參數(shù)個(gè)數(shù)也沒有執(zhí)行檢查。
參考：
http://innig.net/software/ruby/closures-in-ruby
以上結(jié)論驗(yàn)證于最新的ruby1.9.3，和鏈接中的結(jié)論有些許不同；ruby1.8中的proc函數(shù)可能有不同的行為。