C＃中带有类型参数的泛型类型

Question

I don't think that this could be done in C#, but posting this just to make sure. Here's my problem. I would like to do something like this in C#:

var x = 10;
var l = new List<typeof(x)>();

or

var x = 10;
var t = typeof(x);
var l = new List<t>();

But of course this doesn't work. Although this shouldn't be a problem as the type t is resolved at compile time. I understand that this can be solved with reflection, but as types are known at compile time using reflection would be overkill.

Answer 1

public static List<T> CreateCompatibleList<T> (T t)
{
    return new List<T> () ;
}

var x = 10 ;
var l = CreateCompatibleList (x) ;

Answer 2

You're trying to get .Net to set a generic type using a run-time operator. As you know, that won't work. Generics types must be set at compile time.

Answer 3

Defining generics is done like this in C#:

var someList = new List<int>();

You can not define generics like this:

var x = 1;
var someType = typeof(x);
var someList = new List<someType>();

because you're specifying the type at run time in this case, not compile time. C# doesn't support that.

Answer 4

You can't do it exactly how you are asking, but with a little reflection you can accomplish the same thing

Type genericType = typeof(List<>);
Type[] type = new Type[] { typeof(int) };
Type instanceType = genericType.MakeGenericType(type);
object instance = Activator.CreateInstance(instanceType );
var l = (List<int>)instance;