closures

来源： https://stackoverflow.com/questions/62979779/escaping-closure-captures-mutating-self-parameter-firebase

来源： https://stackoverflow.com/questions/62979779/escaping-closure-captures-mutating-self-parameter-firebase

问题 If I do def f(): a = 1 g = lambda: a a = 2 return g print(f()()) The value that is printed is 2 , because a is mutated after g is constructed. How do I get g to capture the value of a statically so that later modifications are ignored? 回答1: For simple cases, such as when the code is short and we don't have many variables to capture, we can create a temporary lambda and call it: def f(): a = 1 g = (lambda a: lambda: a)(a) a = 2 return g The issue here is that the code can quickly become harder

问题 If I do def f(): a = 1 g = lambda: a a = 2 return g print(f()()) The value that is printed is 2 , because a is mutated after g is constructed. How do I get g to capture the value of a statically so that later modifications are ignored? 回答1: For simple cases, such as when the code is short and we don't have many variables to capture, we can create a temporary lambda and call it: def f(): a = 1 g = (lambda a: lambda: a)(a) a = 2 return g The issue here is that the code can quickly become harder

问题 When a closure's resolveStrategy is set to DELEGATE_ONLY or DELEGATE_FIRST , resolution is different in nested closures between methods and properties of the delegate. For example, in the following, x resolves to f 's delegate (what I expect), but keySet() resolves to g 's delegate. ​def g = {-> def f = { {-> [x, keySet()]}() } f.resolveStrategy = Closure.DELEGATE_ONLY f.delegate = [x: 1, f: 0] f() } g.delegate = [x: 0, g: 0] g() ​ Result: [1, ['x', 'g']] Whereas without the nested closure

问题 so I am calling a function that should just return the longitude of an inputted address. I'll append it here so you can look at it and then I will comment on it after the code: func getLongitude(address: String) -> Double { var longitude: Double = 0.0 let geocoder = CLGeocoder() geocoder.geocodeAddressString(address) { placemarks, error in let placemark = placemarks?.first longitude = placemark?.location?.coordinate.longitude ?? 0.0 print("The testing longitude is \(longitude)") } return

问题 so I am calling a function that should just return the longitude of an inputted address. I'll append it here so you can look at it and then I will comment on it after the code: func getLongitude(address: String) -> Double { var longitude: Double = 0.0 let geocoder = CLGeocoder() geocoder.geocodeAddressString(address) { placemarks, error in let placemark = placemarks?.first longitude = placemark?.location?.coordinate.longitude ?? 0.0 print("The testing longitude is \(longitude)") } return

问题 so I am calling a function that should just return the longitude of an inputted address. I'll append it here so you can look at it and then I will comment on it after the code: func getLongitude(address: String) -> Double { var longitude: Double = 0.0 let geocoder = CLGeocoder() geocoder.geocodeAddressString(address) { placemarks, error in let placemark = placemarks?.first longitude = placemark?.location?.coordinate.longitude ?? 0.0 print("The testing longitude is \(longitude)") } return

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x:

问题 I would like to replicate the behavior and ergonomics of taking a closure/function as an argument much like map does: iterator.map(|x| ...) . I've noticed that some library code allows passing in async functionality, but this method doesn't allow me to pass in arguments: pub fn spawn<F, T>(future: F) -> JoinHandle<T> where F: Future<Output = T> + Send + 'static, T: Send + 'static, spawn(async { foo().await }); I'm hoping to do one of the following: iterator.map(async |x| {...}); async fn a(x: