Question

In delphi I can declare a type of class like so

type
  TFooClass = class of TFoo;
  TFoo=class
  end;

Which is the C# equivalent for this declaration?

Answer 1

The closest you can get in C# is the Type type, which contains the metadata about a type.

public class A { }
public static int Main(string[] args)
{
  Type b = typeof(A);
}

It’s not exactly the same. In Delphi, “type of othertype” is itself a type that you can assign to a variable. In C# “type of othertype” is a System.Type instance that can be assigned to any variables of type System.Type.

As an example, in Delphi, you can do this:

type
  TAClass = class of TA;
  TA = class
  public
    class procedure DoSomething;
  end;

var x : TAClass;
begin
  x := TA;
  x.DoSomething();
end;

You cannot do anything like this in C#; you cannot call static methods of type A from instances of Type that happen to hold typeof(A), nor can you define a variable that can only hold typeof(A) or derived types.

(Some specific patterns that Delphi metaclass types are used for, can be accomplished using generics:

public class A { }
public class ListOfA<T> where T: A { } 

In this case, T is the “type of A” or whatever derived class of A was used to construct the class.)