generics

问题 I'm having issues with understanding how matching types in generic functions work in swift. I do not understand why my code is not compiling. This is what I have: enum LoadingState<T> { case idle case loading case failed(Error) case loaded(T) } private func updateInternal(_ state: Int) { print("=int") } private func updateInternal(_ state: String) { print("=string") } private func update<T>(_ state: LoadingState<T>) { switch state { case .loaded(let viewModel): updateInternal(viewModel)

问题 I'm writing an RxJS operator which waits for the input operator to complete and then does a switchMap to a second operator (which is generated on the fly just as with switchMap ). I have come up with two versions of my code, one which works and one which doesn't and I'm struggling to wrap my head around why that is. The version that works: import { Observable } from "rxjs"; // OperatorFunction, import { defaultIfEmpty, last, switchMap } from "rxjs/operators"; // This definition of

问题 I'm reading about Java Generics. and I want to ask what is the difference between the following statements. 1: List<String> list = new ArrayList(3); 2: List<String> list = new ArrayList<String>(2); 3: List<String> list = new ArrayList<String>(); 4a: List<String> list = new ArrayList("A"); // why I can't use String? 4b: List<String> list = new ArrayList('a'); // but char works fine. I'm reading Java Docs on Generics and after that I need to ask the above questions because I didn't get exact

问题 I'm reading about Java Generics. and I want to ask what is the difference between the following statements. 1: List<String> list = new ArrayList(3); 2: List<String> list = new ArrayList<String>(2); 3: List<String> list = new ArrayList<String>(); 4a: List<String> list = new ArrayList("A"); // why I can't use String? 4b: List<String> list = new ArrayList('a'); // but char works fine. I'm reading Java Docs on Generics and after that I need to ask the above questions because I didn't get exact

问题 Service Registration services.AddScoped(typeof(PageStorageService<>), typeof(PageStorageService<>)); Service Declaration public interface IStoredPage<T> { T PageState { get; set; } } public class PageStorageService<T> : IStoredPage<T> { public T PageState { get; set; } } Usage in CounterPage @page "/counter" @using BlazorApp1.Data <h1>Counter</h1> <p>Current count: @currentCount</p> @inject PageStorageService<Counter> StorageService <button class="btn btn-primary" @onclick="IncrementCount"

问题 The following method returns a List composed of T type elements: public <T> List<T> getList() { return new ArrayList<T>(); } In the signature we have <T> List<T> . The List<T> makes sense, because that is the type of the return value . What is the need for the preceding <T> though? The code doesn't compile without both <T> and List<T> . Leaving out the <T> gives Cannot resolve symbol T I have read the official Oracle tutorial on generic methods. It explains that this is part of the syntax:

问题 Scenario: I'm working with an unusual external API in which every attribute is a map with multiple values. In order to convert this response into simple Java objects, I had to do some dirty unboxing. Below is one of the typical java class. As you can see how I'm unboxing data from response and mapping them to my java class: import com.fasterxml.jackson.annotation.JsonProperty; import lombok.*; import java.time.LocalDate; import java.util.Map; import static com.my.util.BaseUtil.unbox; @Getter

问题 I've seen a number of other similar looking questions, but I think there's a level of abstraction on top of those that makes the difference. Namely, I have a utility class with a static generic wrapper method to deserialize an object of generic type (unknown at build time): public final class Utils { public static final Gson sGson = new Gson(); public static synchronized <T> T fromJson(String doc) { return sGson.fromJson(doc, new TypeToken<T>(){}.getType()); } } A simple class to test it on:

问题 I want to have an interface where the generic type is based on the value of a property in this interface: interface Book<T extends BookType> { type: T, location: Shelf<T>, } Instead of using the following to define the generic type: const book: Book<BookType.Technology>; I want const book: Book<???>; book.type = BookType.Technology; And afterwards, location is "hinted" to have type Shelf<BookType.Technology> Is this possible in TypeScript? 回答1: TypeScript doesn't really support making empty

问题 I create an extension for UITableViewCell, and give the default method. Through the set<T: UITableViewCell> method, I want the setupData method can dynamic dispatch by the cell type. But it always failed, and the result jump to the fatalError. import UIKit class cell: UITableViewCell { func setupData<T>(_ data: T) { print(#function) } } class ViewController: UIViewController { override func viewDidLoad() { super.viewDidLoad() set(cell.self) } func set<T: UITableViewCell>(_ t: T.Type) { let