From 0f9454b79b14e46873758642a3f6fd27e954eada Mon Sep 17 00:00:00 2001
From: Mike Gerwitz <mike@mikegerwitz.com>
Date: Sat, 5 Mar 2011 02:59:21 -0500
Subject: [PATCH] interface() no longer returns a usable class - Number of
 reasons. First and foremost, it doesn't make sense to return a usable class
 with no body/definition - Secondly, to make the following commit(s) possible
 and consistent

---
 lib/class.js                 | 52 +++++++++++++++++++++++++++-------
 test/test-class-implement.js | 55 +++++++++++++++++++++++++++++-------
 2 files changed, 87 insertions(+), 20 deletions(-)

diff --git a/lib/class.js b/lib/class.js
index 44c4411..33b8ccf 100644
--- a/lib/class.js
+++ b/lib/class.js
@@ -100,12 +100,11 @@ module.exports.extend = function( base )
  */
 module.exports.implement = function()
 {
-    var args = Array.prototype.slice.call( arguments );
-
-    // apply to an empty (new) object
-    args.unshift( module.exports.extend() );
-
-    return implement.apply( this, args );
+    // implement on empty base
+    return createImplement(
+        module.exports.extend(),
+        Array.prototype.slice.call( arguments )
+    );
 };
 
 
@@ -313,6 +312,37 @@ function createStaging( cname )
 }
 
 
+/**
+ * Creates an intermediate object to permit implementing interfaces
+ *
+ * This object defers processing until extend() is called. This intermediate
+ * object ensures that a usable class is not generated until after extend() is
+ * called, as it does not make sense to create a class without any
+ * body/definition.
+ *
+ * @param  {Object}  base    base class to implement atop of
+ * @param  {Array}   ifaces  interfaces to implement
+ *
+ * @return  {Object}  intermediate implementation object
+ */
+function createImplement( base, ifaces )
+{
+    ifaces.unshift( base );
+
+    // Defer processing until after extend(). This also ensures that implement()
+    // returns nothing usable.
+    return {
+        extend: function( def )
+        {
+            return extend.apply( null, [
+                implement.apply( this, ifaces ),
+                def
+            ] );
+        },
+    };
+}
+
+
 /**
  * Creates extend function
  *
@@ -714,6 +744,8 @@ function attachExtend( func )
 /**
  * Attaches implement method to the given function (class)
  *
+ * Please see the implement() export of this module for more information.
+ *
  * @param  {function()}  func  function (class) to attach method to
  *
  * @return  {undefined}
@@ -722,10 +754,10 @@ function attachImplement( func )
 {
     util.defineSecureProp( func, 'implement', function()
     {
-        var args = Array.prototype.slice.call( arguments );
-        args.unshift( func );
-
-        return implement.apply( this, args );
+        return createImplement(
+            func,
+            Array.prototype.slice.call( arguments )
+        );
     });
 }
 
diff --git a/test/test-class-implement.js b/test/test-class-implement.js
index cfb973a..ff46d61 100644
--- a/test/test-class-implement.js
+++ b/test/test-class-implement.js
@@ -64,19 +64,41 @@ var Type = Interface.extend( {
 {
     assert.doesNotThrow( function()
     {
-        Foo = Class.implement( Type, Type2 );
+        Class.implement( Type, Type2 );
     }, Error, "Class can implement interfaces" );
+} )();
 
-    assert.ok(
-        ( Class.isClass( Foo ) ),
-        "Class returned from implementing interfaces on an empty base is a " +
-            "valid class"
+
+/**
+ * Initially, the implement() method returned an abstract class. However, it
+ * doesn't make sense to create a class without any actual definition (and
+ * there's other implementation considerations that caused this route to be
+ * taken). One wouldn't do "class Foo implements Type", and not provide any
+ * body.
+ *
+ * Therefore, implement() should return nothing useful until extend() is called
+ * on it.
+ */
+( function testResultOfImplementIsNotUsableAsAClass()
+{
+    var result = Class.implement( Type );
+
+    assert.equal(
+        ( Class.isClass( result ) ),
+        false,
+        "Result of implement operation on class is not usable as a Class"
     );
 } )();
 
 
+/**
+ * As a consequence of the above, we must extend with an empty definition
+ * (base) in order to get our abstract class.
+ */
 ( function testAbstractMethodsCopiedIntoNewClassUsingEmptyBase()
 {
+    Foo = Class.implement( Type, Type2 ).extend( {} );
+
     assert.ok(
         ( ( Foo.prototype.foo instanceof Function )
             && ( Foo.prototype.foo2 instanceof Function )
@@ -90,19 +112,32 @@ var Type = Interface.extend( {
 {
     assert.doesNotThrow( function()
     {
-        PlainFoo2 = PlainFoo.implement( Type, Type2 );
+        PlainFoo.implement( Type, Type2 );
     }, Error, "Classes can implement interfaces" );
+} )();
 
-    assert.ok(
-        ( Class.isClass( PlainFoo2 ) ),
-        "Class returned from implementing interfaces on an existing base is a " +
-            "valid class"
+
+/**
+ * Ensure the same system mentioned above also applies to the extend() method on
+ * existing classes
+ */
+( function testImplementingInterfaceAtopExistingClassIsNotUsableByDefault()
+{
+    var result = PlainFoo.implement( Type );
+
+    assert.equal(
+        ( Class.isClass( result ) ),
+        false,
+        "Result of implementing interfaces on an existing base is not " +
+            "usable as a Class"
     );
 } )();
 
 
 ( function testAbstractMethodsCopiedIntoNewClassUsingExistingBase()
 {
+    PlainFoo2 = PlainFoo.implement( Type, Type2 ).extend( {} );
+
     assert.ok(
         ( ( PlainFoo2.prototype.foo instanceof Function )
             && ( PlainFoo2.prototype.foo2 instanceof Function )