A-M baby

Task/Add-a-variable-to-a-class-instance-at-runtime/Icon/add-a-variable-to-a-class-instance-at-runtime.icon

@@ -0,0 +1,27 @@
+link ximage
+
+procedure main()
+   c1 := foo(1,2)                            # instance of foo
+   write("c1:\n",ximage(c1))
+   c1 := extend(c1,["c","d"],[8,9])          # 2 new fields
+   write("new c1:\n",ximage(c1))
+   c1 := extend(c1,["e"],[7])                # 1 more
+   write("newest c1:\n",ximage(c1))
+end
+
+class foo(a,b)                               # dummy class
+end
+
+procedure extend(instance,newvars,newvals)   #: extend a class instance
+   every put(f := [],fieldnames(instance))   # copy existing fieldnames
+   c := ["tempconstructor"] ||| f            # new constructor
+   every put(c,!newvars)                     # append new vars
+   t := constructor!c                        # new constructor
+   x := t()                                  # new instance
+   every x[v := !f] := instance[v]           # same as old instance
+   x.__s := x                                # new self
+   if \newvals then
+      every i := 1 to min(*newvars,*newvals) do
+         x[newvars[i]] := newvals[i]         # add new vars = values
+   return x
+end