Trouble initializing a templated class

[quakkels via Digitalmars-d-learn]

> try SomeClass (T): BaseClass

Not sure which line you want me to change. I don't want SomeClass 
to inherit from BaseClass. Rather, I want T to be restricted to 
classes that inherit from BaseClass.

When I change `class SomeClass(T : BaseClass)` to `class 
SomeClass(T) : BaseClass` I still get the "class 
templateExp.SomeClass(T) is used as a type" error.