>>-FORWARD--+----------+--+------------------------+------------>
+-CONTINUE-+ +-ARGUMENTS--expra-------+
| +-,-----+ |
| V | |
+-ARRAY--(----expri-+--)-+
>--+----------------+--+--------------+--+-----------+---------><
+-MESSAGE--exprm-+ +-CLASS--exprs-+ +-TO--exprt-+
You can specify the options in any order.
FORWARD forwards the message that caused the currently active method to begin running. The FORWARD instruction can change parts of the forwarded message, such as the target object, the message name, the arguments, and the superclass override.
If you specify the TO option, the language processor evaluates exprt to produce a new target object for the forwarded message. The exprt is a literal string, constant symbol, or expression enclosed in parentheses. If you do not specify the TO option, the initial value of the Rexx special variable SELF is used.
If you specify the ARGUMENTS option, the language processor evaluates expra to produce an array object that supplies the set of arguments for the forwarded message. The expra can be a literal string, constant symbol, or expression enclosed in parentheses. The ARGUMENTS value must evaluate to a Rexx array object.
If you specify the ARRAY option, each expri is an expression (use commas to separate the expressions). The language processor evaluates the expression list to produce a set of arguments for the forwarded message. It is an error to use both the ARRAY and the ARGUMENTS options on the same FORWARD instruction.
If you specify neither ARGUMENTS nor ARRAY, the language processor uses the same arguments specified on the original method call.
If you specify the MESSAGE option, the exprm is a literal string, a constant symbol, or an expression enclosed in parentheses. If you specify an expression enclosed in parentheses, the language processor evaluates the expression to obtain its value. The uppercase character string value of the MESSAGE option is the name of the message that the FORWARD instruction issues.
If you do not specify MESSAGE, FORWARD uses the message name used to call the currently active method.
If you specify the CLASS option, the exprs is a literal string, a constant symbol, or an expression enclosed in parentheses. This is the class object used as a superclass specifier on the forwarded message.
If you do not specify CLASS, the message is forwarded without a superclass override.
If you do not specify the CONTINUE option, the language processor immediately exits the current method before forwarding the message. Results returned from the forwarded message are the return value from the original message that called the active method (the caller of the method that issued the FORWARD instruction). Any conditions the forwarded message raises are raised in the calling program (without raising a condition in the method issuing the FORWARD instruction).
If you specify the CONTINUE option, the current method does not exit and continues with the next instruction when the forwarded message completes. If the forwarded message returns a result, the language processor assigns it to the special variable RESULT. If the message does not return a result, the language processor drops (uninitializes) the variable RESULT.
The FORWARD instruction passes all or part of an existing message invocation to another method. For example, the FORWARD instruction can forward a message to a different target object, using the same message name and arguments.
Example 2.16. Instructions - FORWARD
::method substr
forward to (self~string) /* Forward to the string value */
You can use FORWARD in an UNKNOWN method to reissue to another object the message that the UNKNOWN method traps.
Example 2.17. Instructions - FORWARD
::method unknown
use arg msg, args
/* Forward to the string value */
/* passing along the arguments */
forward to (self~string) message (msg) arguments (args)
You can use FORWARD in a method to forward a message to a superclass's methods, passing the same arguments. This is very common usage in object INIT methods.
Example 2.18. Instructions - FORWARD
::class savings subclass account
::method init
expose type penalty
forward class (super) continue /* Send to the superclass */
type = "Savings" /* Now complete initialization */
penalty = "1% for balance under 500"
In the preceding example, the CONTINUE option causes the FORWARD message to continue with the next instruction, rather than exiting the Savings class INIT method.
