Reduce repetitive implementation of the same algorithm in the code. Make sure that insertion happens in one method only

Source/GSOrderedSet.m

@@ -249,21 +249,7 @@ static Class	mutableSetClass;
 
 - (void) addObject: (id)anObject
 {
-  GSIArrayItem item;
-
-  if (anObject == nil)
-    {
-      [NSException raise: NSInvalidArgumentException
-		  format: @"Tried to add nil to set"];
-    }
-
-  if([self containsObject: anObject] == NO)
-    {
-      item.obj = anObject;
-      GSIArrayAddItem(&array, item);
-      RETAIN(anObject);
-      _version++;
-    }
+  [self insertObject: anObject atIndex: [self count]];
 }
 
 - (void) insertObject: (id)object atIndex: (NSUInteger)index
@@ -271,7 +257,8 @@ static Class	mutableSetClass;
   GSIArrayItem item;
   if(object == nil)
     {
-      NSWarnLog(@"Attempt to insert nil object");
+      [NSException raise: NSInvalidArgumentException
+		  format: @"Tried to add nil to set"];
     }
   else
     {
@@ -329,13 +316,7 @@ static Class	mutableSetClass;
 	    }
 	  else
 	    {
-	      GSIArrayItem item;
-	      if(![self containsObject: anObject])
-		{
-		  item.obj = anObject;
-		  GSIArrayAddItem(&array, item);
-		  RETAIN(anObject);
-		}
+	      [self addObject: anObject];
 	    }
 	}
     }

Source/NSOrderedSet.m

@@ -50,6 +50,9 @@
 
 @class	GSMutableOrderedSet;
 @interface GSMutableOrderedSet : NSObject	// Help the compiler
+@end
+
+@interface NSOrderedSet (Private)
 - (void) _raiseRangeExceptionWithIndex: (NSUInteger)index from: (SEL)sel;
 @end
 
@@ -1453,16 +1456,16 @@ static SEL	rlSel;
 		   * first equal object we don't get left with a bad object
 		   * pointer for later comparisons.
 		   */
-		  RETAIN(anObject);
+		  // RETAIN(anObject);
 		}
 	      (*rem)(self, remSel, i);
 	      break;  // since this is a set we should only have one copy...
 	    }
 	}
-      if (rem != 0)
-	{
-	  RELEASE(anObject);
-	}
+      //if (rem != 0)
+      // {
+      //  RELEASE(anObject);
+      // }
     }
 }
 
@@ -1799,7 +1802,7 @@ static SEL	rlSel;
       [self removeAllObjects];
       [self addObjectsFromArray: res];
 
-      RELEASE(res);
+      // RELEASE(res);
       GS_ENDIDBUF();
     } 
 }

Tests/base/NSOrderedSet/basic.m

@@ -338,7 +338,6 @@ int main()
   PASS([[mutableTest4 objectAtIndex: 9] isEqual:@"Flee From"] == YES,
        "replaceObjectsAtIndexes: adds to correct indexes");
 
-
   id uobj = [NSKeyedUnarchiver unarchiveObjectWithData: data];
   PASS((uobj != nil &&
 	[uobj isKindOfClass: [NSMutableOrderedSet class]] &&