closures

问题 Completion handler closures are common in iOS development, such as dataTask(with:completionHandler:) in the URLSession class. The UI engine is managed by the main thread, the API calls by URLSession are run under the background thread and must be dispatched to the main thread if a UI update is needed in the handler. Question 1 : Do all completion handler closures from the iOS framework run in the background thread? Question 1.1 : Do all escaping closures, for example, created by developers,

问题 Is there any kind of performance or other difference between following two cases of accessing a global variable in a closure: Case 1: $closure = function() use ($global_variable) { // Use $global_variable to do something. } Case 2: $closure = function() { global $global_variable; // Use $global_variable to do something. } 回答1: There is an important difference between your two examples: $global_variable = 1; $closure = function() use ($global_variable) { return $global_variable; }; $closure2 =

问题 I noticed that when a variable is captured by a closure in Swift, the closure can actually modify the value. This seems crazy to me and an excellent way of getting horrendous bugs, specially when the same var is captured by several closures. var capture = "Hello captured" func g(){ // this shouldn't be possible! capture = capture + "!" } g() capture On the other hand, there's the inout parameters, which allow a function or closure to modify its parameters. What's the need for inout, even

问题 I would like to do the following in swift code: I have to call my api in order to update several items. So I call the api for each item asynchronously. Each api call executes a callback function when it's done. These callbacks decrease a counter, so that when the counter reaches 0 I know that all my api calls are completed. When the counter reaches 0 I would like to call a final callback function (once, when all calls are complete), in order to update my UI and so forth. This final callback

问题 I would like to do the following in swift code: I have to call my api in order to update several items. So I call the api for each item asynchronously. Each api call executes a callback function when it's done. These callbacks decrease a counter, so that when the counter reaches 0 I know that all my api calls are completed. When the counter reaches 0 I would like to call a final callback function (once, when all calls are complete), in order to update my UI and so forth. This final callback

问题 I'm trying to implement the State monad in Rust ( State is effectively a wrapper over a function which takes original state and returns modified state and some result). This is how one can implement State in Haskell (monad operations where renamed to unit and bind for sake of simplicity): data State s u = State { run :: s -> (u, s) } -- return unit :: u -> State s u unit u = State $ \s -> (u, s) -- (>>=) bind :: State s u -> (u -> State s a) -> State s a bind m f = State $ \s -> let (u, s') =

问题 I need to switch part of my projects from C# to Java. But before which, I would like to compare two languages carefully and completely. Regarding to lambda expression, I could write very elegant code via C#, the question is how to implement the same feature gracefully in Java? Thanks in advance! class Program { enum Gender { Male, Female } class Student { public int Id { get; set; } public string Name { get; set; } public int Age { get; set; } public Gender Gender { get; set; } public

问题 I have a follow-up question to the one discussed here: Laravel core method confusion I am in the same situation as driechel (author of question above) has been before, currently getting used to Laravel 4 FW and examining the core. Although a precise answer has been given I still don't understand the logic and what is happening under the hood. So I would very much appreciate a further explanation. I know this might be a duplicate but since I cannot post comments yet I'll give it a shot with a

问题 Let me ask one question. It's about closures in JavaScript, but not about how they work. David Flanagan in his "JavaScript The Definitive Guide 6th Edition" wrote: ... Technically, all JavaScript functions are closures: they are objects, and they have a scope chain associated with them. ... Is this correct? Can I call every function (function object + it's scope) a "closure"? And stacks' tag "closures" says: A closure is a first-class function that refers to (closes over) variables from the

问题 This question already has answers here : Closed 7 years ago . Possible Duplicate: Javascript closure inside loops - simple practical example Seen many posts talking about setTimeout and closures but I'm still not able to pass in a simple for loop counter. for (i = 0; i < 5; i++) { setTimeout(function () { console.log(i); }, Math.floor(Math.random() * 1000)); } Gives 5 5 5 5 5 Would like to have 0 1 2 3 4 What's wrong ? Please don't flame, I thought I have understood the setTimeout() tale but