[*] Previous commit (property cloning per instance) now applied to subtypes as well

lib/class.js

@@ -109,9 +109,11 @@ var extend = ( function( extending )
         prototype.parent = base.prototype;
 
         // set up the new class
-        var new_class = create_ctor( result_data, properties );
+        var new_class = create_ctor( result_data );
 
         setup_props( new_class, result_data );
+        attach_prop_init( prototype, properties );
+
         new_class.prototype   = prototype;
         new_class.constructor = new_class;
 
@@ -143,15 +145,7 @@ var extend = ( function( extending )
         {
             return function()
             {
-                // initialize each of the properties for this instance to
-                // ensure we're not sharing prototype values
-                var value;
-                for ( prop in properties )
-                {
-                    // initialize the value with a clone to ensure that they do
-                    // not share references (and therefore, data)
-                    this[ prop ] = util.clone( properties[ prop ] );
-                }
+                this.__initProps();
 
                 // call the constructor, if one was provided
                 if ( this.__construct instanceof Function )
@@ -190,6 +184,47 @@ function setup_props( func, class_data )
 }
 
 
+/**
+ * Attaches __propInit() method to the class prototype
+ *
+ * The __propInit() method will initialize class properties for that instance,
+ * ensuring that their data is not shared with other instances (this is not a
+ * problem with primitive data types).
+ *
+ * The __propInit() method will also initialize any parent properties
+ * (recursive) to ensure that subtypes do not have a referencing issue, and
+ * subtype properties take precedence over those of the parent.
+ *
+ * @param  {Object}  prototype   prototype to attach method to
+ * @param  {Object}  properties  properties to initialize
+ *
+ * @return  {undefined}
+ */
+function attach_prop_init( prototype, properties )
+{
+    util.defineSecureProp( prototype, '__initProps', function()
+    {
+        // first initialize the parent's properties, so that ours will overwrite
+        // them
+        var parent_init = prototype.parent.__initProps;
+        if ( parent_init instanceof Function )
+        {
+            parent_init.call( this );
+        }
+
+        // initialize each of the properties for this instance to
+        // ensure we're not sharing prototype values
+        var value;
+        for ( prop in properties )
+        {
+            // initialize the value with a clone to ensure that they do
+            // not share references (and therefore, data)
+            this[ prop ] = util.clone( properties[ prop ] );
+        }
+    });
+}
+
+
 /**
  * Attaches isAbstract() method to the class
  *

test/test-class-extend.js

@@ -166,3 +166,22 @@ assert.ok(
     "Multiple instances of the same class do not share object references"
 );
 
+var arr_val = 1;
+var SubAnotherFoo = AnotherFoo.extend(
+{
+    arr: [ arr_val ],
+});
+
+var SubObj1 = new SubAnotherFoo(),
+    SubObj2 = new SubAnotherFoo();
+
+assert.ok(
+    ( ( SubObj1.arr !== SubObj2.arr ) && ( SubObj1.obj !== SubObj2.obj ) ),
+    "Instances of subtypes do not share property references"
+);
+
+assert.ok(
+    ( ( SubObj1.arr[ 0 ] === arr_val ) && ( SubObj2.arr[ 0 ] === arr_val ) ),
+    "Subtypes can override parent property values"
+);
+