From b8a6aa2af6f4cf7c01c91ddbabf9320ddb50a233 Mon Sep 17 00:00:00 2001
From: Mike Gerwitz <mike@mikegerwitz.com>
Date: Fri, 21 Jan 2011 21:53:31 -0500
Subject: [PATCH] Method builder does not permit overriding properties with
 methods

---
 lib/member_builder.js              | 10 ++++++++++
 test/test-member_builder-method.js | 29 +++++++++++++++++++++++++++++
 2 files changed, 39 insertions(+)

diff --git a/lib/member_builder.js b/lib/member_builder.js
index b28405c..decca44 100644
--- a/lib/member_builder.js
+++ b/lib/member_builder.js
@@ -63,6 +63,16 @@ exports.initMembers = function( mpublic, mprotected, mprivate )
  */
 exports.buildMethod = function( members, meta, name, value, keywords )
 {
+    var prev = scanMembers( members, name );
+
+    // disallow overriding properties with methods
+    if ( prev && !( prev instanceof Function ) )
+    {
+        throw new TypeError(
+            "Cannot override property '" + name + "' with method"
+        );
+    }
+
     getMemberVisibility( members, keywords )[ name ] = value;
 };
 
diff --git a/test/test-member_builder-method.js b/test/test-member_builder-method.js
index 5fb35d3..69feefa 100644
--- a/test/test-member_builder-method.js
+++ b/test/test-member_builder-method.js
@@ -23,6 +23,7 @@
  */
 
 var common    = require( './common' ),
+    assert    = require( 'assert' ),
     mb_common = require( './inc-member_builder-common' )
 ;
 
@@ -32,3 +33,31 @@ mb_common.buildMember = common.require( 'member_builder' ).buildMethod;
 // do assertions common to all member builders
 mb_common.assertCommon();
 
+
+/**
+ * One may question the purpose of this assertion. Why should we not permit
+ * overriding properties with methods? It's useful to be able to store callbacks
+ * and such within properties.
+ *
+ * Yes, it is. However, that would be misinterpreting the purpose of the method
+ * builder. Here, we are working with prototypes, not class instances. If the
+ * user wishes to assign a function to the property (so long as it's permitted
+ * by the type definition) after the class is instantiated, he/she may go right
+ * ahead. However, if we modify the prototype to use a function, then the
+ * prototype will interpret the function as a method. As such, the method cannot
+ * be overridden with a property in the future. To avoid this confusing
+ * scenario, we'll prevent it from occurring entirely.
+ */
+( function testCannotOverridePropertyWithMethod()
+{
+    mb_common.value = 'moofoo';
+    mb_common.buildMemberQuick();
+
+    assert.throws( function()
+    {
+        // attempt to override with function
+        mb_common.value = function() {};
+        mb_common.buildMemberQuick( {}, true );
+    }, TypeError, "Cannot override property with method" );
+} )();
+