langs a-z

Task/Add-a-variable-to-a-class-instance-at-runtime/REBOL/add-a-variable-to-a-class-instance-at-runtime.rebol

@@ -0,0 +1,50 @@
+REBOL [
+	Title: "Add Variables to Class at Runtime"
+	Author: oofoe
+	Date: 2009-12-04
+	URL: http://rosettacode.org/wiki/Adding_variables_to_a_class_instance_at_runtime
+]
+
+; As I understand it, a REBOL object can only ever have whatever
+; properties it was born with. However, this is somewhat offset by the
+; fact that every instance can serve as a prototype for a new object
+; that also has the new parameter you want to add.
+
+; Here I create an empty instance of the base object (x), then add the
+; new instance variable while creating a new object prototyped from
+; x. I assign the new object to x, et voila', a dynamically added
+; variable.
+
+x: make object! [] ; Empty object.
+
+x: make x [
+	newvar: "forty-two" ; New property.
+]
+
+print "Empty object modifed with 'newvar' property:"
+probe x
+
+; A slightly more interesting example:
+
+starfighter: make object! [
+	model: "unknown"
+	pilot: none
+]
+x-wing: make starfighter [
+	model: "Incom T-65 X-wing"
+]
+	
+squadron: reduce [
+	make x-wing [pilot: "Luke Skywalker"]
+	make x-wing [pilot: "Wedge Antilles"]
+	make starfighter [
+		model: "Slayn & Korpil B-wing"
+		pilot: "General Salm"
+	]
+]
+
+; Adding new property here.
+squadron/1: make squadron/1 [deathstar-removal-expert: yes]
+
+print [crlf "Fighter squadron:"]
+foreach pilot squadron [probe pilot]