program Project7 uses Dialogs Controls type TParent class protected Fi

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program Project7;
uses Dialogs, Controls;
type
TParent = class
protected
Field: string;
public
constructor Create; virtual;
procedure VeryComplexAlgo;
end;
TChildA = class(TParent)
public
constructor Create; override;
end;
TChildB = class(TParent)
public
constructor Create; override;
end;
TParentClass = class of TParent;
function GetClassFromUser:TParentClass;
begin
if MessageDlg('Use TChildA?', mtConfirmation, [mbYes, mbNo], 0)=mrYes
then result := TChildA
else result := TChildB
end;
{ TParent }
constructor TParent.Create;
begin
Field := 'TParent'
end;
procedure TParent.VeryComplexAlgo;
begin
ShowMessage(Field)
end;
{ TChildA }
constructor TChildA.Create;
begin
inherited;
Field := Field + ' TChildA';
end;
{ TChildB }
constructor TChildB.Create;
begin
inherited;
Field := Field + ' TChildB';
end;
begin
GetClassFromUser.Create.VeryComplexAlgo
end.