Implement memoize using native Maps

It should offer better performances, by avoiding comparing values using Immutable.is, and removing the small immutable object creation overhead.

src/utils/memoize.js

@@ -1,10 +1,8 @@
 
-import { Map } from 'immutable'
-
 /**
- * The leaf node of a cache tree.
+ * The leaf node of a cache tree. Used to support variable argument length.
  *
- * An object, so that immutable maps will key it by reference.
+ * A unique object, so that native Maps will key it by reference.
  *
  * @type {Object}
  */
@@ -12,12 +10,19 @@ import { Map } from 'immutable'
 const LEAF = {}
 
 /**
- * An unique value used to detect cache misses
+ * A value to represent a memoized undefined value. Allows efficient
+ * value retrieval using Map.get only.
  *
  * @type {Object}
  */
 
-const NO_SET = {}
+const UNDEFINED = {}
+
+/**
+ * Default value for unset keys in native Maps
+ */
+
+const UNSET = undefined
 
 /**
  * Memoize all of the `properties` on a `object`.
@@ -36,23 +41,78 @@ function memoize(object, properties) {
     }
 
     object[property] = function (...args) {
-      const keys = [property, ...args, LEAF]
+      const keys = [property, ...args]
       this.__cache = this.__cache || new Map()
 
-      const cachedValue = this.__cache.getIn(keys, NO_SET)
-      if (cachedValue !== NO_SET) {
-        return cachedValue
+      const cachedValue = getIn(this.__cache, keys)
+      if (cachedValue !== UNSET) {
+        return cachedValue === UNDEFINED ? undefined : cachedValue
       }
 
       const value = original.apply(this, args)
-      // If `original` is recursive, it might have changed the cache,
-      // so read it from this.__cache
-      this.__cache = this.__cache.setIn(keys, value)
+      this.__cache = setIn(this.__cache, keys, value)
       return value
     }
   }
 }
 
+/**
+ * Set a value at a key path in a tree of Map, creating Maps on the go.
+ *
+ * @param{Map} map
+ * @param{Array} keys
+ * @param{Any} value
+ * @return {Map}
+ */
+
+function setIn(map, keys, value) {
+  value = value === undefined ? UNDEFINED : value
+
+  let parentMap = map
+  let childMap
+  for (const key of keys) {
+    childMap = parentMap.get(key)
+
+    if (childMap === UNSET) {
+      // This path was not created yet
+      childMap = new Map()
+      parentMap.set(key, childMap)
+    }
+
+    parentMap = childMap
+  }
+  // The whole map path was created
+
+  // Set the value to the bottom most map
+  childMap.set(LEAF, value)
+
+  return map
+}
+
+/**
+ * Get a value at a key path in a tree of Map.
+ * If not set, returns UNSET.
+ * If the set value is undefined, returns UNDEFINED
+ *
+ * @param{Map} map
+ * @param{Array} keys
+ * @return {Any | UNSET | UNDEFINED}
+ */
+
+function getIn(map, keys) {
+  let childMap
+  for (const key of keys) {
+    childMap = map.get(key)
+    if (childMap === UNSET) {
+      // Not found
+      return UNSET
+    }
+    map = childMap
+  }
+
+  return childMap.get(LEAF)
+}
+
 /**
  * Export.
  */