closures

问题 Python code objects have an attribute co_cellvars. The documentation to PyPy's bytecode interpreter often uses the term Cell . Among other langauges, Rust provides a Cell datatype. Googling suggests they relate to closures somehow. What is a cell , in the context of a programming language implementation? What problem do cells solve? 回答1: In Python, cell objects are used to store the free variables of a closure. Let's say you want a function that always returns a particular fraction of its

问题 This question already has an answer here : Why doesn't my arrow function return a value? (1 answer) Closed last year . So to my understanding which is obviously wrong at this moment in time is that, return arg => arg*2 is the same as return (arg)=>{arg*2} I always assumed arrow functions are just syntactically neater. But doing this with closures like so doesn't work. function addTwoDigits(firstDigit){ return (secondDigit)=>{firstDigit + secondDigit} } let closure = addTwoDigits(5); console

问题 In viewdidload i have below methods: var savedSummonerID : Int? savedSummonerID = LeagueMethodHelper.retrieveSummonerIDFromSummonerName(serverNameAbbreviation, summonerName : summonerName) print("haha \(self.savedSummonerID)") I expect to run methods in order but print statement is actually getting called first. retrieveSummonerIDFromSummonerName is described below: static func retrieveSummonerIDFromSummonerName(serverName : String, summonerName : String) -> Int { var savedSummonerID = 0

问题 I read somewhere that whenever a function gets called, the compiler puts all the visible variables on a stack, somewhat related to closures as well, now with the following code I'm not really sure if it'd work in a concurrent environment like node.js. Product.prototype.list = function(body) { body.options = { hostname: endPoints.product, path: '/applications/' + body.entityType method: 'GET' }; return remote.request(body) .then(function(result){ body[body.entityType] = result; return body; })

问题 I have a question, during study of closure. I want make datatypes closure method like in array types .sort(), .filter(), .reduce(), .map() But how can I make this things. Its datatype not a class. I want make array.somemethod({closure}) not a Somefunc(input: array, closure : { .... }) - Can I make datatype method in swift? otherwise, I can use func only? 回答1: You just need extend Array and pass a closure as your method argument. Lets say you would like to create a mutating method to work as

问题 I'm trying to simplify some JS code that uses closures but I am getting nowhere (probably because I'm not grokking closures) I have some code that looks like this: var server = http.createServer(function (request, response) { var httpmethods = { "GET": function() { alert('GET') }, "PUT": function() { alert('PUT') } }; }); And I'm trying to simplify it in this way: var server = http.createServer(function (request, response) { var httpmethods = { "GET": function() { alertGET() }, "PUT":

问题 I am wondering why the following two snippets output different results. It looks like the iteration counter is a special case handled by closure. int i = 1 def closures = (1..3).collect { return { println i; ++i } } for (int j = 0; j < 3; ++j) { closures += { println j } } closures*.call() 1 2 3 3 3 3 回答1: It's a question of when the variable is updated In the first example, i is only incremented when the closure is executed, so even though each closure is bound to the same instance of i ,

问题 As new to groovy... I'm trying to replace the java idiom for event listeners, filters, etc. My working code in groovy is the following: def find() { ODB odb = ODBFactory.open(files.nodupes); // data nucleus object database Objects<Prospect> src = odb.getObjects(new QProspect()); src.each { println it }; odb.close(); } class QProspect extends SimpleNativeQuery { public boolean match(Prospect p) { if (p.url) { return p.url.endsWith(".biz"); } return false; } } Now, this is far from what I'm

问题 I got into a discussion the other day about some nitty-gritty details of programming languages, and one topic that was brought up was what a function (or closure/lambda/etc.) actually 'is' from a data structures perspective. To be clear, I am not asking what functions do or how they are used, but rather how they are represented in code 'behind the scenes'. When a function is 'called', what is happening as the code executes? Is a function a struct or object of some kind that is passed around

问题 This question already has answers here : Why is my variable unaltered after I modify it inside of a function? - Asynchronous code reference (6 answers) Closed 3 years ago . I am trying to use a variable x defined inside a function P whose value I am trying to set in another function. It always comes undefined. I tried applying my mind to use closure but it's just going off my head. It does not gives me a string rather a object. The logic is as follows. function P(i){ var x; if(i!=null){ /