3 files changed, 46 insertions, 1 deletions
diff --git a/collections/map/map.adoc b/collections/map/map.adoc
index 2b3e2cb..2822b79 100644
--- a/collections/map/map.adoc
+++ b/collections/map/map.adoc
@@ -1,7 +1,7 @@
 Map
 ===
 Tucker Evans
-v0.3, 2020-07-06
+v0.4, 2020-07-06
 
 A basic map implemented in an AVL tree.
 
@@ -92,6 +92,27 @@ map_insert(dict, "ONE", NULL);
 assert(map_size(dict) == 1);
 ----
 
+[[map_reset_key]]
++void* map_reset_key(map *self, vaid *key)+
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+This replaces an equivalent key with the one passed in, the key that is
+overwritten is return so the user can free it.
+
+Examples
+^^^^^^^^
+[source,c]
+----
+#include "map.h"
+#include <string.h>
+
+map *dict = map_new((cmp_func) strcmp);
+
+map_insert(dict, strdup("ONE"), "VALUE");
+assert(map_insert(dict, "ONE", "NEW_VALUE") < 0);
+free(map_reset_key(dict "ONE"));
+assert(map_insert(dict, "ONE", "NEW_VALUE") == 0);
+----
+
 [[map_clear]]
 +void map_clear(map *self)+
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/collections/map/map.c b/collections/map/map.c
index 83a446d..7de58e4 100644
--- a/collections/map/map.c
+++ b/collections/map/map.c
@@ -82,6 +82,29 @@ void *key, *val;
 	return 0;
 }
 
+void* map_reset_key(root, key)
+map *root;
+void *key;
+{
+	void *tmp;
+	int cmp;
+
+	if (!root || !key)
+		return NULL;
+
+	cmp = root->cmp(root->key, key);
+
+	if (cmp < 0)
+		return map_reset_key(root->left, key);
+
+	if (cmp > 0)
+		return map_reset_key(root->right, key);
+
+	tmp = root->key;
+	root->key = key;
+	return tmp;
+}
+
 void map_clear(root)
 map *root;
 {
diff --git a/collections/map/map.h b/collections/map/map.h
index b389d87..a5fc816 100644
--- a/collections/map/map.h
+++ b/collections/map/map.h
@@ -12,6 +12,7 @@ int map_size(map*);
 
 /*data*/
 int map_insert(map*, void*, void*);
+void* map_reset_key(map*, void*);
 
 /*memory*/
 void map_clear(map*);