I have two binary files that contain a similar type of data so I want to create a unified viewer (TViewer) for both files. Some, methods are common for these two file types, some are not. So I created a base class TShape, and the from it TCircle and TTriangle.
Pseudo code:
TShape = class(TObject)
function NoOfItems: integer; virtual; abstract;
end;
TCircle = class(TShape)
function NoOfItems: integer; override; <---- The real implementation
end;
TTriangle = class(TShape)
function NoOfItems: integer; override; <---- The real implementation
end;
TViewer = class(TStringGrid)
Container: TShape;
end;
And I use it like this:
Procedure Main;
begin
if FileType= Circle
then (Viewer.Container as TCircle).Load(FileName)
else (Viewer.Container as TTriangle).Load(FileName);
Caption:= Viewer.Container.NoOfItems; <---- it calls TShape which is abstract
end;
When I do this it works:
if Viewer.Container is TTriangle
then Caption:= (Viewer.Container as TTriangle).NoOfItems
else ...
but I want to do it directly like this:
Caption:= Viewer.Container.NoOfItems;
Obviously there is nothing wrong in using is
except that I will have to use it in many many places (close to everywhere). There is a nicer way to achieve this unified viewer?
Update:
Actually, it may be also a performance problem. My file has a really big number of items (up to billions) so doing so many 'is/as' tests may actually have a real impact on speed.
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