引用传参（摘引自Delphi Basic）

Passing by reference means that the subroutine actually refers to the passed variable rather than its value. Any changes to the value will affect the caller variable. We declare a variable to be passed by reference with the var prefix. Rewriting the above code to use by reference changes matters:

 procedure DoIt(Var A : Integer);

                         begin

                           A := A * 2;

                           ShowMessageFmt('A in the procedure  = %d',[A]);

                         end;

                         

                         procedure TForm1.FormCreate(Sender: TObject);

                         var

                           A : Integer;

                         begin

                           A := 22;

                           ShowMessageFmt('A in program before call = %d',[A]);

                           // Call the procedure

                           DoIt(A);

                           ShowMessageFmt('A in program now = %d',[A]);

                         end;

 A in program before call = 22

                         A in the procedure = 44

                         A in program now = 44

Now the caller A variable is updated by the procedure.

This is a very useful way of returning data from a procedure, as used by, for example, the Delphi Insert routine. It also allows us to return more than one value from a subroutine.