CODEWITHSUNDEEP
c#genericstype-inference
Max
Max

Reputation: 20004

Generic types with type parameter in C#

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.

Upvotes: 14

Views: 5054

Answers (4)

Bob
Bob

Reputation: 99734

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;

Upvotes: 2

Anton Tykhyy
Anton Tykhyy

Reputation: 20076

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

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

Upvotes: 41

Joel Coehoorn
Joel Coehoorn

Reputation: 415820

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.

Upvotes: 6

Joseph
Joseph

Reputation: 25523

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.

Upvotes: 3

Related Questions