closures

问题 I want to write a function to reverse geocode a location and assign the resulting string into a variable. Following this post i've got something like this: extension CLLocation { func reverseGeocodeLocation(completion: (answer: String?) -> Void) { CLGeocoder().reverseGeocodeLocation(self) { if let error = $1 { print("[ERROR] \(error.localizedDescription)") return } if let a = $0?.last { guard let streetName = a.thoroughfare, let postal = a.postalCode, let city = a.locality else { return }

问题 I came across this interesting problem. Write a javascript function that returns sum of all the arguments passed to it, through multiple calls to that same function. Here are the ways function can be called - sum(1, 2, 3, 4); sum(1, 2)(3, 4); sum(1, 2)(3)(4); sum(1, 2, 3)(4); sum(1)(2, 3, 4); All the calls above should work and return 10. Here's what I have written so far, but it only works for first two function calls sum(1, 2, 3, 4) and sum(1, 2)(3, 4) and shits the bed for rest of it.

问题 Well, I recently learned about closures in Javascript. While i find it's concept truly amazing, i have yet to find a good application for them, myself. In all the blog posts, all the tuturials i found, i got a good explanation of what they are and how to work with them. What i can't find anywhere are examples that make me think: "Wow! you can do THIS with closures? Awesome!!!". All the examples i find are purely academic like this one. function say667() { // Local variable that ends up within

问题 Even after reading You don't know JS and JavaScript: The Core I still couldn't understand the behavior of the following code. Why, when I call counter()() , do I get no closure, but if I assign a variable to the result of counter() , like var getClosure = counter() , I then get a closure when calling getClosure() ? function counter() { var _counter = 0; function increase() { return _counter++ } return increase; } // Double ()() to call the returned function always return 0, so no closure.

问题 This question already has an answer here : Assign value of a Firestore document to a variable (1 answer) Closed 1 year ago . I have a FireStore function in my FirestoreService file as below; func retrieveDiscounts() -> [Discount] { var discounts = [Discount]() reference(to: .discounts).getDocuments { (snapshots, error) in if error != nil { print(error as Any) return } else { guard let snapshot = snapshots else { return } discounts = snapshot.documents.compactMap({Discount(dictionary: $0.data(

问题 I want to write a closure that takes an object and returns an iterator from it. The idea is to store the closure in a structure and apply as needed: fn main() { let iter_wrap = |x: &String| Box::new(x.chars()); let test = String::from("test"); for x in iter_wrap(&test) { println!("{}", x); } } This causes the error: error[E0495]: cannot infer an appropriate lifetime for lifetime parameter in function call due to conflicting requirements --> src/main.rs:2:45 | 2 | let iter_wrap = |x: &String|

问题 Assuming I have lots of functions or methods with receiver, each of which has different type of parameters. I want to use table-driven method to dispatch function or method call. So I'll construct a table like this: type command struct { name string handler func(parameter ...interface{}) // I don't know whether to use `...interface{}` is correct } table := map[string]command { ... } func (c command)foo(f1 int, f2 string) {} func (c command)bar(b1 bool, b2 int, b3 string) {} // methods and so

问题 Look at this code: #![feature(async_closure)] use std::future::Future; use std::pin::Pin; trait A<'a> { fn call(&'a self, data: &'a i32) -> Pin<Box<dyn 'a + Future<Output=()>>>; } impl <'a, F, Fut> A<'a> for F where Fut: 'a + Future<Output=()>, F: Fn(&'a i32) -> Fut { fn call(&'a self, data: &'a i32) -> Pin<Box<dyn 'a + Future<Output=()>>> { Box::pin(self(data)) } } async fn sample(_data: &i32) { } fn is_a(_: impl for<'a> A<'a>) { } fn main() { is_a(sample); is_a(async move |data: &i32| {

问题 Look at this code: #![feature(async_closure)] use std::future::Future; use std::pin::Pin; trait A<'a> { fn call(&'a self, data: &'a i32) -> Pin<Box<dyn 'a + Future<Output=()>>>; } impl <'a, F, Fut> A<'a> for F where Fut: 'a + Future<Output=()>, F: Fn(&'a i32) -> Fut { fn call(&'a self, data: &'a i32) -> Pin<Box<dyn 'a + Future<Output=()>>> { Box::pin(self(data)) } } async fn sample(_data: &i32) { } fn is_a(_: impl for<'a> A<'a>) { } fn main() { is_a(sample); is_a(async move |data: &i32| {

问题 When executing the following code I get what I expect when the first loop is done (sequence from 0 to 9). But when the second loop finishes, the result is not what I expected (I expected the same result as in the first loop, but it prints only '10's): package main import ( "fmt" "sync" ) func main() { var wg sync.WaitGroup for i := 0; i < 10; i++ { wg.Add(1) go func(j int) { defer wg.Done() fmt.Println(j) }(i) } wg.Wait() fmt.Println("done first") for i := 0; i < 10; i++ { wg.Add(1) go func()