Generic comparison

[Ola Fosheim Grøstad via Digitalmars-d-learn]

I want to implement a generic function for "a < f(x) < b" that 
will give the same result as "(a < f(x)) && (f(x) < b)" for any 
conceivable mix of types. Except if that "f(x)" should only be 
evaluated once.

Is it sufficient to use "scope ref" in parameters?
I don't want to assume _anything_ about the definition of the 
types and the implementation of the comparison operator (can be 
overloaded).