Encapsulating implemented list (can use isInstanceOf() or a future reflection API)

lib/class.js

@@ -24,6 +24,16 @@
 
 var util = require( './util' );
 
+/**
+ * Stores class metadata internally (ensures data is encapsulated)
+ *
+ * The data in this object is hashed on the class object itself. Therefore, to
+ * look up an item, you would provide the class itself as the property.
+ *
+ * @type  {Object.<Object, { implemented: Array.<string> }>}
+ */
+var class_meta = {};
+
 
 /**
  * Creates a class, inheriting either from the provided base class or the
@@ -66,13 +76,7 @@ exports.implement = function()
     }
 
     var class_new = exports.extend( dest );
-
-    // we cannot reassign the value since it is frozen, so copy the values into
-    // the array
-    while ( implemented[ 0 ] )
-    {
-        class_new.implemented.push( implemented.shift() );
-    }
+    getMeta( class_new ).implemented = implemented;
 
     return class_new;
 };
@@ -130,6 +134,8 @@ exports.isClassInstance = function( obj )
  */
 exports.isInstanceOf = function( type, instance )
 {
+    var meta, implemented, i;
+
     try
     {
         // check prototype chain (with throw an error if type is not a
@@ -141,16 +147,22 @@ exports.isInstanceOf = function( type, instance )
     }
     catch ( e ) {}
 
-    var implemented = type.implemented;
-    if ( implemented instanceof Array )
+    // if no metadata is available, then our remaining checks cannot be
+    // performed
+    if ( !( meta = getMeta( type ) ) )
     {
-        var i = implemented.length;
-        while ( i-- )
+        return false;
+    }
+
+    implemented = meta.implemented;
+    i           = implemented.length;
+
+    // check implemented interfaces
+    while ( i-- )
+    {
+        if ( implemented[ i ] === type )
         {
-            if ( implemented[ i ] === type )
-            {
-                return true;
-            }
+            return true;
         }
     }
 
@@ -272,6 +284,9 @@ var extend = ( function( extending )
         // members at runtime
         util.freeze( new_class );
 
+        // create internal metadata for the new class
+        createMeta( new_class );
+
         // we're done with the extension process
         extending = false;
 
@@ -352,7 +367,6 @@ function setupProps( func, abstract_methods )
 {
     attachAbstract( func, abstract_methods );
     attachExtend( func );
-    attachImplemented( func );
 }
 
 
@@ -452,19 +466,6 @@ function attachExtend( func )
 }
 
 
-/**
- * Attaches empty list that may be populated with the implemented interfaces
- *
- * @param  {Function}  func  function (class) to attach method to
- *
- * @return  {undefined}
- */
-function attachImplemented( func )
-{
-    util.defineSecureProp( func, 'implemented', [] );
-}
-
-
 /**
  * Attaches partially applied isInstanceOf() method to class instance
  *
@@ -483,3 +484,34 @@ function attachInstanceOf( instance )
     util.defineSecureProp( instance, 'isA', method );
 }
 
+
+/**
+ * Initializes class metadata for the given class
+ *
+ * @param  {Class}  obj  class to initialize metadata for
+ *
+ * @return  {undefined}
+ */
+function createMeta( obj )
+{
+    class_meta[ obj ] = {
+        implemented: [],
+    };
+}
+
+
+/**
+ * Returns reference to metadata for the requested class
+ *
+ * Since a reference is returned (rather than a copy), the returned object can
+ * be modified to alter the metadata.
+ *
+ * @param  {Class}  obj  class to retrieve metadata for
+ *
+ * @return  {Object}
+ */
+function getMeta( obj )
+{
+    return class_meta[ obj ];
+}
+

test/test-class-implement.js

@@ -45,24 +45,11 @@ assert.ok(
 var Foo      = {},
     PlainFoo = Class.extend();
 
-assert.ok(
-    ( PlainFoo.implemented instanceof Array ),
-    "Class contains empty list of implemented interfaces if " +
-        "none are implemented"
-);
-
 assert.doesNotThrow( function()
 {
     Foo = Class.implement( Type, Type2 );
 }, Error, "Class can implement interfaces" );
 
-assert.ok(
-    ( ( Foo.implemented[ 0 ] === Type )
-        && ( Foo.implemented[ 1 ] === Type2 )
-    ),
-    "Class contains list of implemented interfaces"
-);
-
 assert.ok(
     ( ( Foo.prototype.foo instanceof Function )
         && ( Foo.prototype.foo2 instanceof Function )