optional

问题 During the test there is a NullPointerException thrown. I tried to debug it and the only thing I worked out was that eventOptional is always null. Just as if Mockito.when().thenReturn() didn't work. Can anybody help? Here's my code for a tested service and for the test itself: @Service public class EventService { @Autowired public EventService(EventRepository eventRepository) { this.eventRepository = eventRepository; } //... public void updateEvent(EventDTO eventDTO) { Optional<Event>

问题 The task is pretty simple, but I've not been able to come up with a good solution yet: a string can contain numbers, dashes and pluses, or only numbers. ^[0-9+-]+$ does most of what I need, except when a user enters garbage like "+-+--+" I've not had luck with regular lookahead, since the dashes and pluses could potentially be anywhere in the string. Valid strings: 234654 24-3+-2 -234 25485+ Invalid: ++--+ 回答1: How about: ^[0-9+-]*[0-9][0-9+-]*$ This ensures that there is at least one digit

问题 I have some code that looks like this: f(a).and_then(|b| { g(b).and_then(|c| { h(c).map(|d| { do_something_with(a, b, c, d) }) }) }) Where f , g , and h return Option values. I need to use all the intermediate values ( a , b , c , and d ) in the do_something_with calculation. The indentation is very deep. Is there a better way to do this? Ideally it would look something like this (which of course doesn't work): try { let b = f(a); let c = g(b); let d = h(c); do_something_with(a, b, c, d) }

问题 I want to increment an Int? Currently I have written this : return index != nil ? index!+1 : nil Is there some prettier way to write this ? 回答1: For the sake of completeness, Optional has a map() method: /// If `self == nil`, returns `nil`. Otherwise, returns `f(self!)`. @warn_unused_result @rethrows public func map<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U? Therefore index != nil ? index! + 1 : nil is equivalent to index.map { $0 + 1 } 回答2: You can call the advanced(by:) function

问题 I want to increment an Int? Currently I have written this : return index != nil ? index!+1 : nil Is there some prettier way to write this ? 回答1: For the sake of completeness, Optional has a map() method: /// If `self == nil`, returns `nil`. Otherwise, returns `f(self!)`. @warn_unused_result @rethrows public func map<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U? Therefore index != nil ? index! + 1 : nil is equivalent to index.map { $0 + 1 } 回答2: You can call the advanced(by:) function

问题 I'm starting with this code: String startingValue = getMyValue(); String finishingValue = ""; if (startingValue != null) { finishingValue = startingValue; } else { System.out.println("Value was null"); } I want to transform it using Java 8 options to something like this: Optional<String> startingOptional = getMyOptional(); String finishingValue = startingOptional .map(value -> value) .orElse(System.out.println("value not found")); My question is: Is there a way to combine Java8 Optional

问题 To get a value from NSUserDefaults I would do something like this: let userDefaults = NSUserDefaults.standardUserDefaults() if let value = userDefaults.objectForKey(key) { print(value) } However, these methods do not return optionals: boolForKey (defaults to false if not set) integerForKey (defaults to 0 if not set) floatForKey (defaults to 0.0 if not set) doubleForKey (defaults to 0.0 if not set) In my app I want to used the saved value of an integer if it has been previously set. And if it

问题 To get a value from NSUserDefaults I would do something like this: let userDefaults = NSUserDefaults.standardUserDefaults() if let value = userDefaults.objectForKey(key) { print(value) } However, these methods do not return optionals: boolForKey (defaults to false if not set) integerForKey (defaults to 0 if not set) floatForKey (defaults to 0.0 if not set) doubleForKey (defaults to 0.0 if not set) In my app I want to used the saved value of an integer if it has been previously set. And if it

问题 Given var maybeInt: Int? how to the following two conditional statements differ? // (1) if let y = maybeInt { y } else { println("Nope") } // (2) if let y = maybeInt? { y } else { println("Nope") } They seem to behave exactly the same. Is the former a short-cut for the latter? 回答1: The second syntax is optional chaining — just with nothing after the chaining operator. It accesses whatever optional comes before it (if the optional is not nil ), allows chaining property accesses or method calls

问题 With Boost I can create an optional in-place with: boost::optional<boost::asio::io_service::work> work = boost::in_place(boost::ref(io_service)); And disengage it with: work = boost::none; With C++14 / experimental support, I can instead construct an optional in-place with: std::experimental::optional<boost::asio::io_service::work> work; work.emplace(boost::asio::io_service::work(io_service)); But I'm at a loss for how to disengage it... 回答1: work = std::experimental::nullopt; should