closures

问题 I've been trying to learn Python, and while I'm enthusiastic about using closures in Python, I've been having trouble getting some code to work properly: def memoize(fn): def get(key): return (False,) def vset(key, value): global get oldget = get def newget(ky): if key==ky: return (True, value) return oldget(ky) get = newget def mfun(*args): cache = get(args) if (cache[0]): return cache[1] val = apply(fn, args) vset(args, val) return val return mfun def fib(x): if x<2: return x return fib(x-1

问题 I don't understand how closure is more powerful than class. It looks like I can achieve the same behavior of closure using class. Any help would be appreciated 回答1: Closures are poor man's objects / Objects are poor man's closure Please see: closures and objects For the lazy: The venerable master Qc Na was walking with his student, Anton. Hoping to prompt the master into a discussion, Anton said "Master, I have heard that objects are a very good thing - is this true?" Qc Na looked pityingly

问题 Is there a way to serialize a lexical closure in Python using the standard library? pickle and marshal appear not to work with lexical closures. I don't really care about the details of binary vs. string serialization, etc., it just has to work. For example: def foo(bar, baz) : def closure(waldo) : return baz * waldo return closure I'd like to just be able to dump instances of closure to a file and read them back. Edit: One relatively obvious way that this could be solved is with some

问题 I have seen anonymous functions inside for loops to induce new scope on the web in one or two places and would like to know if it makes sense. for example: var attr, colors = ['green','blue','red']; for ( attr = 0; attr < colors.length; attr++) { (function() { var colorAttr = colors[attr]; // do something with colorAttr })(); } I understand it has something to do with keeping the scope inside the for loop clean, but in what situations would this be necessary? Would it be good practice to do

问题 When a local (inner) function is declared in JavaScript, there are two options: Declaring with var keyword, assigning to the variable: (function() { var innerFunction1 = function() { ... }; innerFunction1(); }()); Declaring just with the function keyword, without assigning to variable: (function() { function innerFunction2() { ... }; innerFunction2(); }()); I can see one advantage of the second: the function can be declared below the code which calls it so it is easier to separate private

问题 In objective-C my animation bit would look something like this: [UIView animateWithDuration:0.5 animations:^{ [[[_storedCells lastObject] topLayerView] setFrame:CGRectMake(0, 0, swipeableCell.bounds.size.width, swipeableCell.bounds.size.height)]; } completion:^(BOOL finished) { [_storedCells removeLastObject]; }]; If I translate that into Swift it should look something like this: UIView.animateWithDuration(0.5, animations: { self.storedCells[1].topLayerView.frame = CGRectMake(0, 0, cell

问题 Does anybody know, if closures will be in Java 7? 回答1: At Devoxx 2008, Mark Reinhold made it clear that closures will not be included in Java 7. Wait! Closures will be included in Java 7. Mark Reinhold announced this reversal at Devoxx 2009. Belay that! Closures ( lambda expressions ) have been deferred until Java 8. Follow Project Lambda (JSR 335) for more information. 回答2: It is unknown until the Java SE 7 JSR is created (presumably by Danny Coward) and an expert group is formed and the

问题 Is there any way to modify the bound value of one of the variables inside a closure? Look at the example to understand it better. def foo(): var_a = 2 var_b = 3 def _closure(x): return var_a + var_b + x return _closure localClosure = foo() # Local closure is now "return 2 + 3 + x" a = localClosure(1) # 2 + 3 + 1 == 6 # DO SOME MAGIC HERE TO TURN "var_a" of the closure into 0 # ...but what magic? Is this even possible? # Local closure is now "return 0 + 3 + x" b = localClosure(1) # 0 + 3 +1 ==

问题 Is there any way to modify the bound value of one of the variables inside a closure? Look at the example to understand it better. def foo(): var_a = 2 var_b = 3 def _closure(x): return var_a + var_b + x return _closure localClosure = foo() # Local closure is now "return 2 + 3 + x" a = localClosure(1) # 2 + 3 + 1 == 6 # DO SOME MAGIC HERE TO TURN "var_a" of the closure into 0 # ...but what magic? Is this even possible? # Local closure is now "return 0 + 3 + x" b = localClosure(1) # 0 + 3 +1 ==

问题 I noticed when writing an assert in Swift that the first value is typed as @autoclosure() -> Bool with an overloaded method to return a generic T value, to test existence via the LogicValue protocol . However sticking strictly to the question at hand. It appears to want an @autoclosure that returns a Bool . Writing an actual closure that takes no parameters and returns a Bool does not work, it wants me to call the closure to make it compile, like so: assert({() -> Bool in return false}(), "No