How to create a generic list in this wierd case in c#
- by Marc Bettex
Hello,
In my program, I have a class A which is extended by B, C and many more classes. I have a method GetInstance() which returns a instance of B or C (or of one of the other child), but I don't know which one, so the return type of the method is A.
In the method CreateGenericList(), I have a variable v of type A, which is in fact either a B, a C or another child type and I want to create a generic list of the proper type, i.e. List<B> if v is a B or List<C> if v is a C, ...
Currently I do it by using reflection, which works, but this is extremely slow. I wanted to know if there is another way to to it, which doesn't use reflection.
Here is an example of the code of my problem:
class A { }
class B : A { }
class C : A { }
// More childs of A.
class Program
{
static A GetInstance()
{
// returns an instance of B or C
}
static void CreateGenericList()
{
A v = Program.GetInstance();
IList genericList = // Here I want an instance of List<B> or List<C> or ... depending of the real type of v, not a List<A>.
}
}
I tried the following hack. I call the following method, hoping the type inferencer will guess the type of model, but it doesn't work and return a List<A>. I believe that because c# is statically typed, T is resolved as A and not as the real type of model at runtime.
static List<T> CreateGenericListFromModel<T>(T model) where T : A
{
return new List<T> ();
}
Does anybody have a solution to that problem that doesn't use reflection or that it is impossible to solve that problem without reflection?
Thank you very much,
Marc
