Added support for mixing in traits using use method on a base class

lib/class.js

@@ -376,7 +376,7 @@ function createUse( base, traits )
         {
             var args     = Array.prototype.slice.call( arguments ),
                 dfn      = args.pop(),
-                base = args.pop();
+                ext_base = args.pop();
 
             // "mix" each trait into the provided definition object
             for ( var i = 0, n = traits.length; i < n; i++ )
@@ -384,7 +384,7 @@ function createUse( base, traits )
                 traits[ i ].__mixin( dfn );
             }
 
-            var C    = extend.call( null, base, dfn ),
+            var C    = extend.call( null, ( base || ext_base ), dfn ),
                 meta = ClassBuilder.getMeta( C );
 
             // add each trait to the list of implemented types so that the
@@ -495,6 +495,7 @@ function setupProps( func )
 {
     attachExtend( func );
     attachImplement( func );
+    attachUse( func );
 }
 
 
@@ -544,3 +545,24 @@ function attachImplement( func )
     });
 }
 
+
+/**
+ * Attaches use method to the given function (class)
+ *
+ * Please see the `use' export of this module for more information.
+ *
+ * @param  {function()}  func  function (class) to attach method to
+ *
+ * @return  {undefined}
+ */
+function attachUse( func )
+{
+    util.defineSecureProp( func, 'use', function()
+    {
+        return createUse(
+            func,
+            Array.prototype.slice.call( arguments )
+        );
+    } );
+}
+

test/Trait/MixedExtendTest.js

@@ -136,4 +136,43 @@ require( 'common' ).testCase(
         // o mixes in Tb
         this.assertOk( this.Class.isA( Tb, o ) );
     },
+
+
+    /**
+     * This alternative syntax mixes a trait directly into a base class and
+     * then omits the base class as an argument to the extend method; this
+     * syntax is most familiar with named classes, but we are not testing
+     * named classes here.
+     */
+    'Can mix in traits directly atop of existing class': function()
+    {
+        var called_foo = false,
+            called_bar = false,
+            called_baz = false;
+
+        var C = this.Class(
+        {
+            'public foo': function() { called_foo = true; },
+        } );
+
+        var T = this.Sut(
+        {
+            'public bar': function() { called_bar = true; },
+        } );
+
+        // we must ensure not only that we have mixed in the trait, but that
+        // we have also maintained C's interface and can further extend it
+        var inst = C.use( T ).extend(
+        {
+            'public baz': function() { called_baz = true; },
+        } )();
+
+        inst.foo();
+        inst.bar();
+        inst.baz();
+
+        this.assertOk( called_foo );
+        this.assertOk( called_bar );
+        this.assertOk( called_baz );
+    },
 } );