Add Stack#size.

lodash.js

@@ -1900,8 +1900,8 @@
      * @memberOf Hash
      */
     function hashClear() {
-      this.size = 0;
       this.__data__ = nativeCreate ? nativeCreate(null) : {};
+      this.size = 0;
     }
 
     /**
@@ -2004,8 +2004,8 @@
      * @memberOf ListCache
      */
     function listCacheClear() {
-      this.size = 0;
       this.__data__ = [];
+      this.size = 0;
     }
 
     /**
@@ -2258,7 +2258,8 @@
      * @param {Array} [entries] The key-value pairs to cache.
      */
     function Stack(entries) {
-      this.__data__ = new ListCache(entries);
+      var data = this.__data__ = new ListCache(entries);
+      this.size = data.size;
     }
 
     /**
@@ -2270,6 +2271,7 @@
      */
     function stackClear() {
       this.__data__ = new ListCache;
+      this.size = 0;
     }
 
     /**
@@ -2282,7 +2284,11 @@
      * @returns {boolean} Returns `true` if the entry was removed, else `false`.
      */
     function stackDelete(key) {
-      return this.__data__['delete'](key);
+      var data = this.__data__,
+          result = data['delete'](key);
+
+      this.size = data.size;
+      return result;
     }
 
     /**
@@ -2322,16 +2328,18 @@
      * @returns {Object} Returns the stack cache instance.
      */
     function stackSet(key, value) {
-      var cache = this.__data__;
-      if (cache instanceof ListCache) {
-        var pairs = cache.__data__;
+      var data = this.__data__;
+      if (data instanceof ListCache) {
+        var pairs = data.__data__;
         if (!Map || (pairs.length < LARGE_ARRAY_SIZE - 1)) {
           pairs.push([key, value]);
+          this.size = ++data.size;
           return this;
         }
-        cache = this.__data__ = new MapCache(pairs);
+        data = this.__data__ = new MapCache(pairs);
       }
-      cache.set(key, value);
+      data.set(key, value);
+      this.size = data.size;
       return this;
     }
 
@@ -10343,7 +10351,7 @@
       return memoized;
     }
 
-    // Assign cache to `_.memoize`.
+    // Expose `MapCache`.
     memoize.Cache = MapCache;
 
     /**