Fix fred's suggestions. Put guard and make more general method the one which is called.

Headers/Foundation/NSKeyedArchiver.h

@@ -88,6 +88,7 @@ extern "C" {
 + (NSData*) archivedDataWithRootObject: (id)anObject;
 
 
+#if OS_API_VERSION(MAC_OS_X_VERSION_10_13,GS_API_LATEST)
 /**
  * Encodes anObject and returns the resulting data object.  Allows
  * secure coding if specified.  Returns an error if an object 
@@ -96,6 +97,7 @@ extern "C" {
 + (NSData *) archivedDataWithRootObject: (id)anObject
                   requiringSecureCoding: (BOOL)requiresSecureCoding
                                   error: (NSError **)error;
+#endif
 
 /**
  * Encodes anObject and writes the resulting data ti aPath.

Source/NSKeyedArchiver.m

@@ -430,16 +430,27 @@ static NSDictionary *makeReference(unsigned ref)
 
 @implementation	NSKeyedArchiver
 
-/*
- * When I tried this on MacOS 10.3 it encoded the object with the key 'root',
- * so this implementation does the same.
- */
 + (NSData *) archivedDataWithRootObject: (id)anObject
+                  requiringSecureCoding: (BOOL)requiresSecureCoding
+                                  error: (NSError **)error
+{
+  NSData *d = nil;
+
+  if (requiresSecureCoding == YES)
+    {
+      if (error != NULL)
+        {
+          *error = [NSError errorWithDomain: @"NSKeyedArchiver"
+                                       code: 0
+                                   userInfo: nil];
+        }
+    }
+  else
     {
       NSMutableData	*m = nil;
       NSKeyedArchiver	*a = nil;
-  NSData		*d = nil;
 
+      error = NULL;
       NS_DURING
         {
           m = [[NSMutableData alloc] initWithCapacity: 10240];
@@ -456,29 +467,22 @@ static NSDictionary *makeReference(unsigned ref)
           DESTROY(a);
           [localException raise];
         }
-  NS_ENDHANDLER
+      NS_ENDHANDLER;
+    }
+
   return AUTORELEASE(d);
 }
 
+/*
+ * When I tried this on MacOS 10.3 it encoded the object with the key 'root',
+ * so this implementation does the same.
+ */
 + (NSData*) archivedDataWithRootObject: (id)anObject
-                  requiringSecureCoding: (BOOL)requiresSecureCoding
-                                  error: (NSError **)error
 {
-  NSData *data = nil;
+  return [self archivedDataWithRootObject: anObject
-  if (requiresSecureCoding == YES)
+                    requiringSecureCoding: NO
-    {
+                                    error: NULL];
-      *error = [NSError errorWithDomain: @"NSKeyedArchiver"
-                                   code: 0
-                               userInfo: nil];
 }
-  else
-    {
-      error = NULL;
-      data = [self archivedDataWithRootObject: anObject];
-    }
-  return data;
-}
-
 
 + (BOOL) archiveRootObject: (id)anObject toFile: (NSString*)aPath
 {