The default mode for a method parameter is input. An input parameter passes a value to the method but does not return a value from the method. Thus, an input parameter can be a database field, an expression, or a variable.
Caution: Do not use the INPUT keyword as a mode option because, for a parameter, ABL might interpret this as the screen value of a widget.
The mode option OUTPUT or INPUT-OUTPUT specifies a parameter that returns a value from the method. (An INPUT-OUTPUT parameter also passes a value to the method.) This means that the value of any passed variable can change after the method call returns. You can only specify the OUTPUT or INPUT-OUTPUT options with a variable as the parameter (as opposed to a database field or an expression):
DEFINE VARIABLE MyWallet AS DECIMAL NO-UNDO.
myObject:WithdrawMoneyPtr(OUTPUT MyWallet AS CURRENCY).
Note: The OUTPUT or INPUT-OUTPUT option forces the parameter to be passed as a pointer and explicitly specifies that a value be returned to your application. Thus, if you use a mode option, you do not need to use the BY-POINTER type option because the type option is redundant. However, the BY-POINTER type option, by itself, does not return a value to your program. You must use a mode option or ABL does not allow the method to return a value in the parameter.
Note that ABL does not use Type Library information to determine the parameter mode. This prevents the COM object from updating a variable that you do not expect or want to change. Thus, if the COM object ordinarily changes the value of a particular parameter, you can prevent any variable you pass from having its value changed by omitting any mode option on the parameter.
