Forward Declarations and Mutually Dependent Classes

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.

Forward declarations allow mutually dependent classes. For example, type

TFigure = class; // forward declaration TDrawing = class

Figure: TFigure;

end;

TFigure = class // defining declaration

Drawing: TDrawing; end;

Do not confuse forward declarations with complete declarations of types that derive from TObject without declaring any class members.

type

TFirstClass = class; // this is a forward declaration TSecondClass = class // this is a complete class declaration end; //

TThirdClass = class(TObject); // this is a complete class declaration

Project Management Made Easy

Project Management Made Easy

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