closures

问题 I have see the following code... The first call of (next-num) returns 1 , and the second returns 2 . (define next-num (let ((num 0)) (lambda () (set! num (+ num 1)) num))) (next-num) ; 1 (next-num) ; 2 What I can not understand is... num is created by let inside next-num , it is kind of a local variable... How does scheme know that each time next-num is called, the value of num is not erased by let ((num 0)) ; How does scheme know that it is always the same num that we modify whenever next

问题 In the Swift documentation Apple says this: Closures are self-contained blocks of functionality that can be passed around and used in your code. Closures in Swift are similar to blocks in C and Objective-C and to lambdas in other programming languages. Which I thought was the definition of First-class functions And they also say this: Closures can capture and store references to any constants and variables from the context in which they are defined. This is known as closing over those

问题 I am going through the How to make a chain of function decorators? to understand decorator. In the following example, we see that "method_to_decorate" is accessible to wrapper function because of closures. But, I didn't understand how arguments self and lie are accessible to the wrapper function. def method_friendly_decorator(method_to_decorate): def wrapper(self, lie): lie = lie - 3 # very friendly, decrease age even more :-) return method_to_decorate(self, lie) return wrapper class Lucy

问题 In order to make my code easier to read, I am using type aliases in Swift for various types of closures. I have the following basic set of closures: public typealias FailureClosure = (error: NSError?) -> Void public typealias ProgressClosure = (progress: Float32) -> Void public typealias BasicClosure = () -> Void I would like to add a closure typealias that supports generic arrays, but I can't seem to figure out the syntax for it. This is as far as I am able to get, but I get the compile time

问题 I am making a game in HTML5, and now I just got a disturbing problem. In my game I have an Array with all the particles, all the particles have expire-timers, with different random generated delays. When the expire-timers expire they delete there own Object with the Array.splice() function, that causes trouble, since the Array.splice() function will mess up the order of the Array. First I had the function like this: (n = Blood particles to spawn, and x and y = starting point.) (All particles

问题 I am looking for some of the difference/purpose of autoclosure and escaping closure in Swift. I know well that an escaping closure is something we want to execute after the function has been returned but I didn't get the concept of an autoclosure. 回答1: I didn't get the concept of autoclosure closure. The autoclosure allows a function to wrap an expression in a closure so that it can be executed later or not at all. A good example of the use of an autoclosure is the short-circuit behavior that

问题 We have been debating how best to handle objects in our JS app, studying Stoyan Stefanov's book, reading endless SO posts on 'new', 'this', 'prototype', closures etc. (The fact that there are so many, and they have so many competing theories, suggests there is no completely obvious answer). So let's assume the we don't care about private data . We are content to trust users and developers not to mess around in objects outside the ways we define. Given this , what (other than it seeming to

问题 I have done abit of research on stackoverflow and apple's documentation about ARC and Weak/Unowned self (Shall we always use [unowned self] inside closure in Swift). I get the basic idea about strong reference cycle and how it is not good as they cause memory leaks. However, I am trying to get my head around when to use Weak/Unowned self in closures. Rather then going into the "theory", I think it would really really help if someone could kindly explain them in terms of the bottom three cases

问题 i am kinda confused reading the definition between the two. Can they actually intersect in terms of definition? or am i completely lost? Thanks. 回答1: Closures, as the word tends to be used, are just functions (or blocks of code, if you like) that you can treat like a piece of data and pass to other functions, etc. (the "closed" bit is that wherever you eventually call it, it behaves just as it would if you called it where it was originally defined). A monad is (roughly) more like a context in

问题 for (var i = 0; i < somearray.length; i++) { myclass.foo({'arg1':somearray[i][0]}, function() { console.log(somearray[i][0]); }); } How do I pass somearray or one of its indexes into the anonymous function ? somearray is already in the global scope, but I still get somearray[i] is undefined 回答1: The i in the anonymous function captures the variable i , not its value . By the end of the loop, i is equal to somearray.length , so when you invoke the function it tries to access an non-existing