如何在不知道类型参数的情况下声明通用类型的变量？

Question

How do I define a generic TList type so that I can declare a variable of that type and then assign any specialization of TList<> to it?

I want to declare this variable:

var
  MyList:THowToDeclareThisListType<T>;

And then instantiate it like this:

MyList:=THowToDeclareThisListType<integer>.Create;

or

MyList:=THowToDeclareThisListType<double>.Create;

etc. I must be missing something pretty obvious here. I don't want classes, just a simple type definition.

Answer 1

You are trying to declare a variable like this:

var
  List: TList<?>;

such that List can be assigned objects of type TList<Integer> or TList<Double> or TList<string> .

That is not possible. When you define a variable using a generic type, the type must be fully instantiated.

The only way that you can have a variable that holds any object of type TList<T> is if the variable is declared to have a common base class to TList<T> . And the common base class cannot be a non-instantiated generic. For TList<T> the only possible common base class is TObject .

So you could write

var
  List: TObject;

and then assign any of your objects to List . But I'm not sure that would be terribly useful!