# http://mantis.bearnip.com/view.php?id=475

Consider this code:

  mixed x = m_allocate(100,2); x += ([2:3;4;5]);
  mixed y = m_allocate(100,2); y = y + ([2:3;4;5]);

The first line results in an error, saying the mapping width doesn't match. The second line results in y containing mapping of width 3. As x is empty, the first line should work as well.

add_to_mapping() in mapping.c tests for empty mappings with
    0 == m2->num_entries && NULL == m2->hash
For m_allocate-d mappings, hash is empty but not 0.

Why is the hash tested at all? 3.2 doesn't have that check.

Attachment: patch to remove the NULL == m[1,2]->hash tests

Index: mapping.c
===================================================================
--- mapping.c	(revision 2306)
+++ mapping.c	(working copy)
@@ -3352,7 +3352,7 @@
         /* If one of the two mappings is empty, we can adjust its width
          * after getting rid of all pending data blocks.
          */
-        if (0 == m2->num_entries && NULL == m2->hash)
+        if (0 == m2->num_entries)
         {
             if (m2->cond != NULL)
             {
@@ -3363,7 +3363,7 @@
             }
             m2->num_values = m1->num_values;
         }
-        else if (0 == m1->num_entries && NULL == m1->hash)
+        else if (0 == m1->num_entries)
         {
             if (m1->cond != NULL)
             {