closures | 易学教程

Passing an object property into a closure in PHP

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问题 I am trying to pass an object property into a closure (that's within a method of that object), like so: class Entity extends ControllerBase { private $view; private $events; public function print($tid) { self::loadView($tid); self::loopView(); return (new StreamedResponse(function() use ($this->events){ ... } } } The $events property gets instantiated in the loopView() method. This seems like it should work to me, but I get this error: ParseError: syntax error, unexpected '->' (T_OBJECT

Is it the right way using `[weak self]` in swift closure?

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问题 I always using [weak self] in swift closure to prevent reference cycle. Here is the code below, is it the correct way? someTask(completion: {[weak self] (result) in if self == nil { return } //is it safe when reach here? self!.xxx = yyy self!.doLongTermWork() self!.finish() //will crash when self is nil? }) Weak self does not keep a strong hold on the instance. So when self.doLongTermWork() , will self be set to nil again somewhere else? 回答1: Your pattern has race condition. If self was

function declaration after return statement global variable is not overwritten

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I have a Javascript code as below, http://jsfiddle.net/ramchiranjeevi/63uML/ var foo = 1; function bar() { foo = 10; return; function foo() {} } bar(); console.log(foo); // returns 1 When the code executed, the bar() function is called and the global variable is overwritten with value 10, then the log should be printed as 10 instead it is printed as value 1. Because of a concept called "hoisting", function declarations are "moved" to the top of the scope. When that happens, a new foo context is created within the local scope. The assignment of 10 later affects the localized scope and not the

Trouble with non-escaping closures in Swift 3

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问题 I have an extension Array in the form of: extension Array { private func someFunction(someClosure: (() -> Int)?) { // Do Something } func someOtherFunction(someOtherClosure: () -> Int) { someFunction(someClosure: someOtherClosure) } } But I'm getting the error: Passing non-escaping parameter 'someOtherClosure' to function expecting an @escaping closure . Both closures are indeed non-escaping (by default), and explicitly adding @noescape to someFunction yields a warning indicating that this is

Result of call is unused

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问题 Right below the second comment, I receive an error of "Result of call to 'taskForDeleteMethod' is unused. Why is this when I use the results and error in the closure following the call? func deleteSession(_ completionHandlerForDeleteSession: @escaping (_ success: Bool, _ error: NSError?) -> Void) { /* 1. Specify parameters, method (if has {key}), and HTTP body (if POST) */ // There are none... /* 2. Make the request */ taskForDELETEMethod { (results, error) in /* 3. Send the desired value(s)

cell_contents in python closure

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问题 Has the cell_contents call for closures in python changed? I understand that func_closure does not work and __closure__ works. func.__closure__.cell_contents Traceback (most recent call last): File "<stdin>", line 1, in <module> AttributeError: 'tuple' object has no attribute 'cell_contents' I am using Python 3.4.1. 回答1: Has the cell_contents call for closures in python changed? __closure__ is, and always has been, a tuple of cells (even back when it was called func_closure ). Each cell still

Why is the value moved into the closure here rather than borrowed?

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问题 The Error Handling chapter of the Rust Book contains an example on how to use the combinators of Option and Result . A file is read and through application of a series of combinators the contents are parsed as an i32 and returned in a Result<i32, String> . Now, I got confused when I looked at the code. There, in one closure to an and_then a local String value is created an subsequently passed as a return value to another combinator. Here is the code example: use std::fs::File; use std::io:

Binding click event handlers in a loop causing problems in jQuery

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问题 I am trying to run the following code: I pass parameter to a function, but it always has the value of the last object run through the loop. I read some articles about it on stackoverflow, but I couldn't find out how to make it run in my solution. The object is a JSON object returned from the server. All it's values are correct. for(var i = 0;i<parents.length;i++){ var row = $(document.createElement("tr")); var colName = $(document.createElement("td")); var aDisplayCol = $(document

“Mutable variable is accessible from closure” in a function passed to Array.prototype.every

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问题 Code will speak more plainly than I will: var candidateIndex = 0; var minValue = Number.MAX_VALUE; topArray.every(function(element, index) { if (element.innerArray && element.innerArray.length < minValue) { minValue = element.innerArray.length; candidateIndex = index; if (minValue == 0) { return false; } } return true; }); // ... use minValue and candidateIndex What this is doing is going through the topArray , and finding either the first member of that array that has an innerArray of length

Function pointers working as closures in C++

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问题 Is there a way in C++ to effectively create a closure which will be a function pointer? I am using the Gnu Scientific Library and I have to create a gsl_function. This function needs to effectively "close" a couple of parameters available when I create it. Is there a nice trick to create a closure so that I don't have to pass all of them as params in the gsl_function structure? If not, should I just pass in a pointer to an array containing these parameters? EDIT I have tried to use boost: