return unknown Generic List<T>

Question

and thanks for any assistance.

How would I return from a method an unknown Generic.List type.

public void Main() {   List<A> a= GetData("A");    }  public List<T> GetData(string listType) {    if(listType == "A")    {      List<A> a= new List<A>()       ...      return a;     }    else    {      List<B> b = new List<B>()      return b;     } } 

In the below example I recieve an error similar to: Can't Convert List<A> to List<T>

Is this possible? The error occurs on the 'return a;' line of code.
Also, What will I need to do to make sure an error does not occur on the line:

List<A> a= GetData("A");    

Thanks, Steven

Answer 1

Use IList instead of List<T>.

Answer 2

An alternative to being limited to returning a list of objects would be to either ensure that A and B derive from a common base type or implement a common interface, then return a list of that base type or interface. Include a constraint on the Generic method to that effect:-

List<ICommon> GetData<T>() where T: ICommon {  }