Add memoize functionality

rpg-docs/lib/memoize/memoize.js

@@ -0,0 +1,45 @@
+Tracker.memoize = function(func, hasher){
+	var memoize  = function(key) {
+		var cache = memoize.cache;
+		var address = "" + (hasher ? hasher.apply(this, arguments) : key);
+		if (!_.has(cache, address)) {
+			cache[address] = new CacheObject(func, address, arguments, cache, this);
+		}
+		return cache[address].get();
+	};
+	memoize.cache = {};
+	return memoize;
+};
+
+function CacheObject(func, address, args, cache, context){
+	var self = this;
+	self.currentValue = null;
+	self.dep = new Tracker.Dependency();
+
+	//spawn a new autorun that keeps the value up-to-date
+	Tracker.nonreactive(function() {
+		Tracker.autorun(function(computation) {
+			//if this isn't the first run and nobody is listening,
+			//delete itself from cache and stop the computation
+			if (!computation.firstRun && !self.dep.hasDependents()){
+				computation.stop();
+				delete cache[address];
+				console.log("Nothing depends on '" + address + "', deleting");
+			}
+			//call the expensive function
+			var newValue = func.apply(context, args);
+			//if the value changed, store the new value
+			if (self.currentValue !== newValue){
+				self.currentValue = newValue;
+				//tell the dependents that we've changed
+				self.dep.changed();
+			}
+		});
+	});
+}
+
+CacheObject.prototype.get = function() {
+	//if there is an active computation, track dependents
+	if (Tracker.active) this.dep.depend();
+	return this.currentValue;
+};