optional

问题 Im trying to put the RoomEntity Class in the List as its generic parameter but the List Class turns red(Error) and the only thing that it suggests is for me to change the List Class to Optional Class. public interface RoomRepository extends CrudRepository<RoomEntity, Long> { List<RoomEntity> findById(Long id); } RoomEntity Class @Entity @Table(name = "Room") public class RoomEntity { } are they the same? List<RoomEntity> findById(Long id); Optional<RoomEntity> findById(Long id); 回答1: Optional

问题 Im trying to put the RoomEntity Class in the List as its generic parameter but the List Class turns red(Error) and the only thing that it suggests is for me to change the List Class to Optional Class. public interface RoomRepository extends CrudRepository<RoomEntity, Long> { List<RoomEntity> findById(Long id); } RoomEntity Class @Entity @Table(name = "Room") public class RoomEntity { } are they the same? List<RoomEntity> findById(Long id); Optional<RoomEntity> findById(Long id); 回答1: Optional

问题 I am working on one of the examples in The Swift Programming Language book related to Optional Protocol Requirements. I have a problem in the following code. import Foundation @objc protocol CounterDataSource { optional func incrementForCount(count: Int) -> Int optional var fixedIncrement: Int { get } } @objc class Counter { var count = 0 var dataSource: CounterDataSource? func increment() { if let amount = dataSource?.incrementForCount?(count) { count += amount } else if let amount =

问题 I´m trying to build a type in F#, where when I get an object of that type I can be sure it´s in a valid state. The type is called JobId and it just holds a Guid . The business rule is: It must be a Guid - but no empty Guid. I´ve already implemented the type in C# but now I would like to port it to a F# class library. That´s the C# type: public sealed class JobId { public string Value { get; } private JobId(string value) => Value = value; public static JobId Create() => new JobId(Guid.NewGuid(

问题 I´m trying to build a type in F#, where when I get an object of that type I can be sure it´s in a valid state. The type is called JobId and it just holds a Guid . The business rule is: It must be a Guid - but no empty Guid. I´ve already implemented the type in C# but now I would like to port it to a F# class library. That´s the C# type: public sealed class JobId { public string Value { get; } private JobId(string value) => Value = value; public static JobId Create() => new JobId(Guid.NewGuid(

问题 I´m trying to build a type in F#, where when I get an object of that type I can be sure it´s in a valid state. The type is called JobId and it just holds a Guid . The business rule is: It must be a Guid - but no empty Guid. I´ve already implemented the type in C# but now I would like to port it to a F# class library. That´s the C# type: public sealed class JobId { public string Value { get; } private JobId(string value) => Value = value; public static JobId Create() => new JobId(Guid.NewGuid(

问题 I am new in Swift and don't have much more idea on optional (! , ?). I tried to fetch data from plist, create Model and show to UITableView . Table data shows perfectly, but it shows with Optional() binding. I tried change ! to ? but unable to unwrap. Could you please, guide me to solve this problem. Here is my code & output - var fileName : String? var dataArray : Array<SHQuesAns>? For fetch data from pList - func loadTableView(){ dataArray = SHDataAccess.init(fname: fileName).arrayFromPlist

问题 I am developing some code using Scala and I am trying to smartly resolve a basic transformation between collections that contains some Option[T] . Let's say that we have the following list val list: List[(A, Option[B])] = // Initialization stuff and we want to apply a transformation to list to obtain the following list val transformed: List[(B, A)] for all Option[B] s that evaluate to Some[B] . The best way I found to do this is to apply the following chain of transformations: val transformed

问题 I understand how optionals work, but this is throwing me for a loop. I have a variable called num and I want to increment it, so I did the following: var num:Int! = 0 num++ //ERROR - Unary operator ++ cannot be applied to an operand of type Int! But for some reason Swift won't let me increment a force unwrapped Int , even though it is supposed to be treated like a regular Int with the capability for nil behind the scenes. So I tried the following, and it worked: var num:Int! = 0 num = num + 1

问题 So I have been using Guava's Optional for a while now, and I moving to Java 8 so I wanted to use it's Optional class, but it doesn't have my favorite method from Guava, asSet(). Is there a way to do this with the Java 8 Optional that I am not seeing. I love being able to treat optional as a collection so I can do this: for( final User u : getUserOptional().asSet() ) { return u.isPermitted(getPermissionRequired()); } In some cases avoids the need for an additional variable. IE Optional<User>