generics

问题 I've been trying and trying to make my generic extension methods work, but they just refuse to and I can't figure out why . This thread didn't help me, although it should. Of course I've looked up how to, everywhere I see they say it's simple and it should be in this syntax: (On some places I read that I need to add "where T: [type]" after the parameter decleration, but my VS2010 just says that's a syntax error.) using System.Collections.Generic; using System.ComponentModel; public static

问题 I am trying to create forms that inherit from a "generic" base class where the generic argument of that base class has a constraint that it must implement one of my interfaces. It compiles and runs just fine. My problem is with the Visual Studio designer. It will open the form fine until I rebuild the project, after which it then reports the error below when trying to view the form designer until such time as I either restart Visual Studio, or remove the custom interface constraint in the

问题 I have a function that sometimes has to return a Date other times a DateTime (Joda-Time). static public <T extends Object> T convertTimeForServer(DateTime toSave) { DateTime temp = null; try { temp = toSave.withZone(DateTimeZone.forID(getServerTimeZone())); } catch (Exception e) { } T toReturn = null; if (toReturn.getClass().equals(temp)) { return (T) temp;//Return DATETIME } else { return (T) temp.toDate();//Return DATE } } Is it the right approach? How to use it? like this (timerHelper is

问题 I've had a bit of a problem trying to bind a generic list to a repeater. The type used in the generic list is actually a struct. I've built a basic example below: struct Fruit { public string FruitName; public string Price; // string for simplicity. } protected void Page_Load(object sender, EventArgs e) { List<Fruit> FruitList = new List<Fruit>(); // create an apple and orange Fruit struct and add to List<Fruit>. Fruit apple = new Fruit(); apple.FruitName = "Apple"; apple.Price = "3.99";

问题 I'm trying to get the method name of a function passed into an object using a .Net closure like this: Method Signature public IEnumerable<T> GetData<T>(Func<IEnumerable<T>> WebServiceCallback) where T : class { // either gets me '<LoadData>b__3' var a = nrdsWebServiceCallback.Method.Name; var b = nrdsWebServiceCallback.GetInvocationList(); return WebServiceCallback(); } I'm calling it like this: SessionStateService.Labs = CacheManager.GetData(() => WCFService.GetLabs(SessionStateService.var1,

问题 I have the following swift class with a NumericType T. @objc class MathStatistics<T: NumericType> : NSObject { var numbers = [T]() func sum() -> T? { if numbers.count == 0 { return nil } var sum = T(0) for value in numbers { sum = sum + value } return sum } } In swift a initialize the class object as follows: let statistics = MathStatistics<Double>() How do I initialize the same object in Objective C? The following line does not set the numeric type T. MathStatistics *stats = [[MathStatistics

问题 I have a question on the use of wildcards in Java's generic types: what is the basic difference between List<? extends Set> and List<T extends Set> ? When would I use either? 回答1: Two reasons: To avoid unnecessary casts: You have to use the T variant for cases like this: public <T extends Set> T firstOf(List<T> l) { return l.get(0); } With ? this would become: public Set firstOf2(List<? extends Set> l) { return l.get(0); } ...which doesn't give the same amount of information to the caller of

问题 public class BusinessObjects<O> where O : BusinessObject { void SomeMethod() { var s = O.MyStaticMethod(); // <- How to do this? } } public class BusinessObject { public static string MyStaticMethod() { return "blah"; } } Is there a correct object oriented approach to accomplishing this or will I need to resort to reflection? EDIT: I went too far in trying to oversimplify this for the question and left out an important point. MyStaticMethod uses reflection and needs the derived type to return

问题 I have outer generic class which has some inner class, for which I'd like to use the generic type of outer class. However, I don't understand how to use generic parameters correctly. Example: class Outer<E extends CharSequence>{ class Inner extends ArrayList<E>{ } void func() { ArrayList<CharSequence> al = new ArrayList<CharSequence>(); al.add("abc"); // OK CharSequence a = al.get(0); // OK Inner in = new Inner(); in.add("abc"); // Error: The method add(E) in the type ArrayList<E> is not

问题 This question already has an answer here : How to cast generic types that I know to be integers? (1 answer) Closed 9 months ago . I would like to write something like the following in rust: pub struct Point<T> { pub x: T, pub y: T, } impl<T> Point<T> { pub fn from<U>(other: Point<U>) -> Point<T> { Point { x: other.x as T, y: other as T, } } } This is not possible: error[E0605]: non-primitive cast: `U` as `T` --> src/lib.rs:9:16 | 9 | x: other.x as T, | ^^^^^^^^^^^^ | = note: an `as`