Use a map to back meta's cache.

This is a first step to making the baking store of `Meta`'s
`readableCache` / `writableCache` swappable. The first implementation is
using a simple array of key value pairs, but since we are using the
`set`, `get`, `has`, `delete` interface we can change the backing data
store at will (or even "upgrade" at runtime).

The underlying implementation of the "lodash-stack" is mostly copied
from lodash itself (with inline attribution), but in the longer term we
should simply use this from lodash itself (and embed these modules from
lodash-es in our build process).

Author: rwjblue

packages/ember-metal/lib/chains.js

@@ -182,8 +182,8 @@ function lazyGet(obj, key) {
   // Otherwise attempt to get the cached value of the computed property
   } else {
     let cache = meta.readableCache();
-    if (cache && key in cache) {
-      return cache[key];
+    if (cache && cache.has(key)) {
+      return cache.get(key);
     }
   }
 }

packages/ember-metal/lib/computed.js

@@ -317,8 +317,8 @@ ComputedPropertyPrototype.didChange = function(obj, keyName) {
   }
 
   let cache = meta.readableCache();
-  if (cache && cache[keyName] !== undefined) {
-    cache[keyName] = undefined;
+  if (cache && cache.get(keyName) !== undefined) {
+    cache.set(keyName, undefined);
     removeDependentKeys(this, obj, keyName, meta);
   }
 };
@@ -330,8 +330,8 @@ ComputedPropertyPrototype.get = function(obj, keyName) {
 
   let meta = metaFor(obj);
   let cache = meta.writableCache();
+  let result = cache.get(keyName);
 
-  let result = cache[keyName];
   if (result === UNDEFINED) {
     return undefined;
   } else if (result !== undefined) {
@@ -340,9 +340,9 @@ ComputedPropertyPrototype.get = function(obj, keyName) {
 
   let ret = this._getter.call(obj, keyName);
   if (ret === undefined) {
-    cache[keyName] = UNDEFINED;
+    cache.set(keyName, UNDEFINED);
   } else {
-    cache[keyName] = ret;
+    cache.set(keyName, ret);
   }
 
   let chainWatchers = meta.readableChainWatchers();
@@ -401,10 +401,12 @@ ComputedPropertyPrototype._set = function computedPropertySet(obj, keyName, valu
   // either there is a writable cache or we need one to update
   let cache          = meta.writableCache();
   let hadCachedValue = false;
+  let rawCachedValue = cache.get(keyName);
   let cachedValue;
-  if (cache[keyName] !== undefined) {
-    if (cache[keyName] !== UNDEFINED) {
-      cachedValue = cache[keyName];
+
+  if (rawCachedValue !== undefined) {
+    if (rawCachedValue !== UNDEFINED) {
+      cachedValue = rawCachedValue;
     }
     hadCachedValue = true;
   }
@@ -419,17 +421,17 @@ ComputedPropertyPrototype._set = function computedPropertySet(obj, keyName, valu
   propertyWillChange(obj, keyName);
 
   if (hadCachedValue) {
-    cache[keyName] = undefined;
+    cache.set(keyName, undefined);
   }
 
   if (!hadCachedValue) {
     addDependentKeys(this, obj, keyName, meta);
   }
 
   if (ret === undefined) {
-    cache[keyName] = UNDEFINED;
+    cache.set(keyName, UNDEFINED);
   } else {
-    cache[keyName] = ret;
+    cache.set(keyName, ret);
   }
 
   propertyDidChange(obj, keyName);
@@ -444,9 +446,9 @@ ComputedPropertyPrototype.teardown = function(obj, keyName) {
   }
   let meta = metaFor(obj);
   let cache = meta.readableCache();
-  if (cache && cache[keyName] !== undefined) {
+  if (cache && cache.get(keyName) !== undefined) {
     removeDependentKeys(this, obj, keyName, meta);
-    cache[keyName] = undefined;
+    cache.set(keyName, undefined);
   }
 };
 
@@ -569,7 +571,7 @@ export default function computed(func) {
 function cacheFor(obj, key) {
   var meta = peekMeta(obj);
   var cache = meta && meta.source === obj && meta.readableCache();
-  var ret = cache && cache[key];
+  var ret = cache && cache.get(key);
 
   if (ret === UNDEFINED) {
     return undefined;
@@ -579,22 +581,22 @@ function cacheFor(obj, key) {
 
 cacheFor.set = function(cache, key, value) {
   if (value === undefined) {
-    cache[key] = UNDEFINED;
+    cache.set(key, UNDEFINED);
   } else {
-    cache[key] = value;
+    cache.set(key, value);
   }
 };
 
 cacheFor.get = function(cache, key) {
-  var ret = cache[key];
+  var ret = cache.get(key);
   if (ret === UNDEFINED) {
     return undefined;
   }
   return ret;
 };
 
 cacheFor.remove = function(cache, key) {
-  cache[key] = undefined;
+  cache.set(key, undefined);
 };
 
 export {

packages/ember-metal/lib/meta.js

@@ -7,6 +7,8 @@ import { protoMethods as listenerMethods } from 'ember-metal/meta_listeners';
 import EmptyObject from 'ember-metal/empty_object';
 import { lookupDescriptor } from 'ember-metal/utils';
 import symbol from 'ember-metal/symbol';
+import LodashishStack from './utils/lodash-stack';
+
 
 /**
 @module ember-metal
@@ -92,7 +94,11 @@ function ownMap(name, Meta) {
   let key = memberProperty(name);
   let capitalized = capitalize(name);
   Meta.prototype['writable' + capitalized] = function() {
-    return this._getOrCreateOwnMap(key);
+    let ret = this[key];
+    if (!ret) {
+      ret = this[key] = new LodashishStack();
+    }
+    return ret;
   };
   Meta.prototype['readable' + capitalized] = function() { return this[key]; };
 }

packages/ember-metal/lib/utils/lodash-stack.js

@@ -0,0 +1,79 @@
+/*
+ From Lodash's private ListCache here:
+
+ https://github.com/lodash/lodash/blob/4.13.1/dist/lodash.js#L1790-L1900
+
+ The long term plan is to replace this and simply utilize lodash itself (via
+ rollup or other) in the build itself.
+
+ ***********************************************************************
+ * @license
+ * lodash <https://lodash.com/>
+ * Copyright jQuery Foundation and other contributors <https://jquery.org/>
+ * Released under MIT license <https://lodash.com/license>
+ * Based on Underscore.js 1.8.3 <http://underscorejs.org/LICENSE>
+ * Copyright Jeremy Ashkenas, DocumentCloud and Investigative Reporters & Editors
+ ***********************************************************************
+
+*/
+function assocIndexOf(array, key) {
+  var length = array.length;
+  while (length--) {
+    if (array[length][0] === key) {
+      return length;
+    }
+  }
+
+  return -1;
+}
+
+export default class ListCache {
+  constructor() {
+    this.__data__ = [];
+  }
+
+  clear() {
+    this.__data__ = [];
+  }
+
+  delete(key) {
+    let data = this.__data__;
+    let index = assocIndexOf(data, key);
+
+    if (index < 0) {
+      return false;
+    }
+    var lastIndex = data.length - 1;
+    if (index == lastIndex) {     // jshint ignore:line
+      data.pop();
+    } else {
+      data.splice(index, 1);
+    }
+
+    return true;
+  }
+
+  get(key) {
+    let data = this.__data__;
+    let index = assocIndexOf(data, key);
+
+    return index < 0 ? undefined : data[index][1];
+  }
+
+  has(key) {
+    return assocIndexOf(this.__data__, key) > -1;
+  }
+
+  set(key, value) {
+    let data = this.__data__;
+    let index = assocIndexOf(data, key);
+
+    if (index < 0) {
+      data.push([key, value]);
+    } else {
+      data[index][1] = value;
+    }
+
+    return this;
+  }
+}

packages/ember-metal/lib/weak_map.js

@@ -39,11 +39,12 @@ WeakMap.prototype.get = function(obj) {
   if (meta) {
     let map = meta.readableWeak();
     if (map) {
-      if (map[this._id] === UNDEFINED) {
+      let value = map.get(this._id);
+      if (value === UNDEFINED) {
         return undefined;
       }
 
-      return map[this._id];
+      return value;
     }
   }
 };
@@ -64,7 +65,7 @@ WeakMap.prototype.set = function(obj, value) {
     value = UNDEFINED;
   }
 
-  metaFor(obj).writableWeak()[this._id] = value;
+  metaFor(obj).writableWeak().set(this._id, value);
 
   return this;
 };
@@ -79,7 +80,7 @@ WeakMap.prototype.has = function(obj) {
   if (meta) {
     let map = meta.readableWeak();
     if (map) {
-      return map[this._id] !== undefined;
+      return map.get(this._id) !== undefined;
     }
   }
 
@@ -93,7 +94,7 @@ WeakMap.prototype.has = function(obj) {
  */
 WeakMap.prototype.delete = function(obj) {
   if (this.has(obj)) {
-    delete metaFor(obj).writableWeak()[this._id];
+    metaFor(obj).writableWeak().delete(this._id);
     return true;
   } else {
     return false;

packages/ember-runtime/lib/system/core_object.js

@@ -936,8 +936,8 @@ CoreObject.reopen({
     if (value instanceof ComputedProperty) {
       var cache = meta(this.constructor).readableCache();
 
-      if (cache && cache._computedProperties !== undefined) {
-        cache._computedProperties = undefined;
+      if (cache && cache.get('_computedProperties') !== undefined) {
+        cache.set('_computedProperties', undefined);
       }
     }
   }