Zitat von
Die Delphi-Hilfe:
If the declaration of a class type ends with the word class and a semicolon - that is, if it has the form
type className = class;
with no ancestor or class members listed after the word class, then it is a forward declaration. A forward declaration must be resolved by a defining declaration of the same class within the same type declaration section. In other words, between a forward declaration and its defining declaration, nothing can occur except other type declarations.