generics

问题 I have a generic method that accepts any type as its parameter. For example, I would like a pointcut that matches the calls made to the method only with 'String' type as its parameter. Ultimately the requirement is to limit the scope which the advices get executed for to 'String' parameters. Here is my generic class and method: public class Param<T> { public T execute(T s){ return s; } } Main class: My app makes calls to the method with both Boolean and String as parameters. public static

问题 I'm trying to create a generic consumer widget that facilitates the ViewModel to its child. therefor I have two functions. one that has a function(T) after init of the ViewModel and the other for passing the model to its child Widget. in the generic class is a child of ChangeNotifier and that works fine until I want to send the T value in the two Functions. then I get the following errors: type '(OnBoardingViewModel) => Null' is not a subtype of type '(ChangeNotifier) => void' and type '

问题 Is there any way to set new generic in React.memo? For example, for class components, I can use // set generic class GenericClass<G extends string | number> extends PureComponent {} // and use like this <GenericClass<number> /> In the below scenario, I want to make type G generic. type G = string; const MemoComponent = memo<{ value: G; onValueChange: (newValue: G) => void }>( ({ value, onValueChange }) => { return ( <select onClick={() => { // do calculation onValueChange(value); }} > Button

问题 I want to write kind of function factory. It should be a function, which is called once which different strategies as parameters. It should return a function, which selects one of this strategies dependent on the parameter, which is to be fulfilled by a predicate. Well, better look at condition3 for better understanding. The problem is, that it is not compiling. I think because the compiler can't figure out, that the functional interface H can be realized by the implementation. Without

问题 Reading a Previous SO Question I was confused to find Eric Lippert saying that an interface cannot be defined in C# for all Monads, using an implementation as below: typeInterface Monad<MonadType<A>> { static MonadType<A> Return(A a); static MonadType<B> Bind<B>(MonadType<A> x, Func<A, MonadType<B>> f); } My problem is all the problems listed in the question seem to have easy solutions: no "higher kinded types" => use parent interfaces no static method in interface. => why use static?! just

问题 Reading a Previous SO Question I was confused to find Eric Lippert saying that an interface cannot be defined in C# for all Monads, using an implementation as below: typeInterface Monad<MonadType<A>> { static MonadType<A> Return(A a); static MonadType<B> Bind<B>(MonadType<A> x, Func<A, MonadType<B>> f); } My problem is all the problems listed in the question seem to have easy solutions: no "higher kinded types" => use parent interfaces no static method in interface. => why use static?! just

问题 Reading a Previous SO Question I was confused to find Eric Lippert saying that an interface cannot be defined in C# for all Monads, using an implementation as below: typeInterface Monad<MonadType<A>> { static MonadType<A> Return(A a); static MonadType<B> Bind<B>(MonadType<A> x, Func<A, MonadType<B>> f); } My problem is all the problems listed in the question seem to have easy solutions: no "higher kinded types" => use parent interfaces no static method in interface. => why use static?! just

问题 Is it possible to implement a class constrained to two unique generic parameters? If it is not, is that because it is unimplemented or because it would be impossible given the language structure (inheritance)? I would like something of the form: class BidirectionalMap<T1,T2> where T1 != T2 { ... } I am implementing a Bidirectional dictionary. This is mostly a question of curiosity, not of need. Paraphrased from the comments: Dan: "What are the negative consequence if this constraint is not

问题 Is it possible to use an "OR" condition using Swift's if let ? Something like (for a Dictionary<String, AnyObject> dictionary): if let value = dictionary["test"] as? String or as? Int { println("WIN!") } 回答1: This would make no sense, how would you be able to tell whether value is an Int or a String when you only have one if statement? You can however do something like this: let dictionary : [String : Any] = ["test" : "hi", "hello" : 4] if let value = dictionary["test"] where value is Int ||

问题 I have this for loop, p is a NSManagedObject , fathers is a to-many relationship, so I need to cast NSMutableOrderedSet to [Family] but it does not work, why? for f in p.fathers as [Family] { } 回答1: You can obtain an array representation of the set via the array property - then you can downcast it to the proper type and assign to a variable: let families = p.fathers.array as [Family] but of course you can also use it directly in the loop: for f in p.fathers.array as [Family] { .... } 回答2: The