Added support for named abstract subclasses

lib/class_abstract.js

@@ -39,7 +39,16 @@ module.exports = exports = function()
     markAbstract( arguments );
 
     // forward everything to Class
-    return Class.apply( this, arguments );
+    var result = Class.apply( this, arguments );
+
+    // if we're using the temporary object, then override its methods to permit
+    // abstract classes
+    if ( !Class.isClass( result ) )
+    {
+        abstractOverride( result );
+    }
+
+    return result;
 };
 
 
@@ -64,16 +73,9 @@ exports.extend = function()
  */
 exports.implement = function()
 {
-    var impl   = Class.implement.apply( this, arguments ),
+   var impl = Class.implement.apply( this, arguments );
-        extend = impl.extend;
-
-    // wrap extend, applying the abstract flag
-    impl.extend = function()
-    {
-        markAbstract( arguments );
-        return extend.apply( this, arguments );
-    };
 
+    abstractOverride( impl );
     return impl;
 };
 
@@ -100,3 +102,23 @@ function markAbstract( args )
     }
 }
 
+
+/**
+ * Overrides object members to permit abstract classes
+ *
+ * @param  {Object}  obj  object to override
+ *
+ * @return  {undefined}
+ */
+function abstractOverride( obj )
+{
+    var extend = obj.extend;
+
+    // wrap extend, applying the abstract flag
+    obj.extend = function()
+    {
+        markAbstract( arguments );
+        return extend.apply( this, arguments );
+    };
+}
+

lib/class_builder.js

@@ -1004,7 +1004,7 @@ exports.isInstanceOf = function( type, instance )
 
     try
     {
-        // check prototype chain (with throw an error if type is not a
+        // check prototype chain (will throw an error if type is not a
         // constructor (function)
         if ( instance instanceof type )
         {

test/test-class-abstract.js

@@ -106,14 +106,27 @@ var common = require( './common' ),
 } )();
 
 
-( function testAbstractClassContainsExtendMethod()
+/**
+ * Just as Class contains an extend method, so should AbstractClass.
+ */
+( function testAbstractClassExtendMethodReturnsNewClass()
 {
     assert.ok( typeof AbstractClass.extend === 'function',
         "AbstractClass contains extend method"
     );
+
+    assert.ok(
+        Class.isClass(
+            AbstractClass.extend( { 'abstract foo': [] } )
+        ),
+        "Abstract class extend method returns class"
+    );
 } )();
 
 
+/**
+ * Just as Class contains an implement method, so should AbstractClass.
+ */
 ( function testAbstractClassContainsImplementMethod()
 {
     assert.ok( typeof AbstractClass.implement === 'function',
@@ -363,3 +376,51 @@ var ConcreteFoo = Class.extend( AbstractFoo,
     }, Error, "Should not throw error if overriding a prototype method" );
 } )();
 
+
+/**
+ * Ensure we support named abstract class extending
+ */
+( function testCanCreateNamedAbstractSubtypes()
+{
+    assert.doesNotThrow( function()
+    {
+        var cls = AbstractClass( 'NamedSubFoo' ).extend( AbstractFoo, {} );
+    }, Error, "Can create named abstract subtypes" );
+} )();
+
+
+/**
+ * Abstract classes, when extended, should yield a concrete class by default.
+ * Otherwise, the user should once again use AbstractClass to clearly state that
+ * the subtype is abstract.
+ */
+( function testExtendingAbstractClassIsNotAbstractByDefault()
+{
+    var cls_named  = AbstractClass( 'NamedSubFoo' ).extend( AbstractFoo, {} ),
+        anon_named = AbstractClass.extend( AbstractFoo, {} );
+
+    // named
+    assert.throws(
+        function()
+        {
+            // should throw an error, since we're not declaring it as abstract
+            // and we're not providing a concrete impl
+            Class.isAbstract( cls_named.extend( {} ) );
+        },
+        TypeError,
+        "Extending named abstract classes should be concrete by default"
+    );
+
+    // anonymous
+    assert.throws(
+        function()
+        {
+            // should throw an error, since we're not declaring it as abstract
+            // and we're not providing a concrete impl
+            Class.isAbstract( AbstractFoo.extend( {} ) );
+        },
+        TypeError,
+        "Extending anonymous abstract classes should be concrete by default"
+    );
+} )();
+