Have a template function register(T)() instantiated and executed at startup for all sub classes of a specific base class?

[TwoOfCups]

This is a pretty open ended question here, there very well may 
not be any way to do what I am trying to do with the constraints 
I have. I am curious if anyone can think of something clever here.

So pretty much my goal here is some kind of automatic type 
registry for a specific set of classes. It's something like an 
entity component system. I need it to be a template function to 
do compile time reflection on the classes for serialization and 
things like that.

The ideal end result would be that I could simply do:

```
class Sub : Base {}
```

And Sub would be registered automatically. Primarily it is this 
that I am curious if there is **ANY** way to make happen. If I 
have to start inserting mixins and stuff then I can imagine all 
sorts of ways to make it work, but if I want the end result to be 
**as** clean as possible I can't think of a way to make it work.

Something that is **so so so freakin** close to working is the 
following:

```
class regTclass(T){
	pragma(crt_constructor)
	extern(C)
	static void reg(){
		writeln("Registering type ", T.stringof);
	}
}

class Base {
	this(this T)(){
		pragma(msg, "Base: Subclass is ", T.stringof);
		alias r = regTclass!(T);
	}
}

class Sub : Base {}
```

The above will work for one level of inheritance. An instance of 
regTclass!Sub will be created and the reg call will be called at 
start up auto magically. The flaw is it only works for one level, 
a class SubSub : Sub {} will not get registered.

Is there any way to resolve this flaw? Is there some other route 
I could take that doesn't require a mixin?

I know I can just insert a mixin and do it that way but I want 
things to look as clean as possible. Even that tiny amount of 
boiler plate bothers me a lot and this is a foundational system 
so that boiler plate will be multiplied hundreds of times I am 
expecting. Probably in the end I will just have to get over my 
aesthetic hang ups but I figured a forum post was worth a shot.