OK, humor me on this, I'm trying to follow along.

In Smalltalk, as in most other OO languages, when you describe a class  
that requires another class, you do so with a specific, explicit reference:

myVar := SomeClass new.

Your object is now dependent on SomeClass. In compiled languages, this  
isn't a big deal because, hey, your code ain't gonna compile if SomeClass  
isn't available. (With some exceptions for dynamically loaded libraries, I  
suppose.)

But in Smalltalk, where formal parameters are untyped and the called code  
doesn't, in fact, care what's been passed to it as long as it can answer  
the right messages. Smalltalk doesn't do anything to check this until  
runtime, either.

So this sort of begs the question (to me) of why the class needs to be  
dependent. We could, of course, allow the client to set myVar rather than  
doing it in the code, but why couldn't SomeClass be defined as "any class  
that supports the interface I need to operate"? That would really be more  
Small-talky than what currently exists.

That might exacerbate the whole absent/present thing, dunno.