As others have said, it will only work when T is constrained to be a reference type. Without any constraints, you can compare with null, but only null – and that comparison will always be false for non-nullable value types. Instead of calling Equals, it’s better to use an IComparer<T> – and if you have … Read more
This rule is intended to avoid conflicts in legacy code that still uses raw types. Here’s an illustration of why this was not allowed, drawn from the JLS. Suppose, before generics were introduced to Java, I wrote some code like this: class CollectionConverter { List toList(Collection c) {…} } You extend my class, like this: … Read more
Actually, you can do what you want. If you want to provide multiple interfaces or a class plus interfaces, you have to have your wildcard look something like this: <T extends ClassA & InterfaceB> See the Generics Tutorial at sun.com, specifically the Bounded Type Parameters section, at the bottom of the page. You can actually … Read more
Well, if the method expects an IEnumerable you’ve got to pass something that is a list, even if it contains one element only. passing new[] { item } as the argument should be enough I think
C# does not support this. Hejlsberg has described the reasons for not implementing the feature in an interview with Bruce Eckel: And it’s not clear that the added complexity is worth the small yield that you get. If something you want to do is not directly supported in the constraint system, you can do it … Read more
As mentioned by others, the reason why get(), etc. is not generic because the key of the entry you are retrieving does not have to be the same type as the object that you pass in to get(); the specification of the method only requires that they be equal. This follows from how the equals() … Read more
void foo<TOne, TTwo>() where TOne : BaseOne where TTwo : BaseTwo More info here: http://msdn.microsoft.com/en-us/library/d5x73970.aspx
In order to create an instance of a generic type in a function you must constrain it with the “new” flag. public static string GetAllItems<T>(…) where T : new() However that will only work when you want to call the constructor which has no parameters. Not the case here. Instead you’ll have to provide another … Read more
You could do: var list = new[] { o, o1 }.ToList(); There are lots of ways of skinning this cat, but basically they’ll all use type inference somewhere – which means you’ve got to be calling a generic method (possibly as an extension method). Another example might be: public static List<T> CreateList<T>(params T[] elements) { … Read more
Yes, pretty much. List<T> is a generic class. It supports storing values of a specific type without casting to or from object (which would have incurred boxing/unboxing overhead when T is a value type in the ArrayList case). ArrayList simply stores object references. As a generic collection, List<T> implements the generic IEnumerable<T> interface and can … Read more