michael@0: function f(o) {
michael@0:     var res = 0;
michael@0:     for (var i=0; i<11000; i++) {
michael@0:         res += o.x;
michael@0:     }
michael@0:     return res;
michael@0: }
michael@0: 
michael@0: function O(x) {
michael@0:     if (x)
michael@0:         this.x = 10;
michael@0: }
michael@0: 
michael@0: f(new O(true));
michael@0: 
michael@0: // "o.x" is now missing so the idempotent cache should invalidate f.
michael@0: f(new O(false));