Mercurial > hg > ucx / file diff

--- a/docs/Writerside/topics/map.h.md	Wed Nov 05 22:39:39 2025 +0100
+++ b/docs/Writerside/topics/map.h.md	Wed Nov 05 23:04:46 2025 +0100
@@ -324,6 +324,11 @@
         cx_clone_func clone_func,
         const CxAllocator *clone_allocator,
         void *data);
+
+int cxMapUnion(CxMap *dst, const CxMap *src,
+        cx_clone_func clone_func,
+        const CxAllocator *clone_allocator,
+        void *data);
 ```
 
 With `cxMapClone()` you can create deep copies of the values in one map and insert them into another map.
@@ -337,6 +342,11 @@
 This is equivalent to computing the set difference for the set of keys.
 Likewise, `cxMapIntersection()` and `cxMapListIntersection()` only clone an element from the source map,
 when the key is contained in _both_ collections.
+The function `cxMapUnion()` only clones elements from `src` to `dst` when their key is not present in `dst`.
+
+> The function `cxMapUnion()` does not operate on three maps for the sake of simplicity.
+> If you want to combine two maps without modifying either of them, you can first use `cxMapClone()`
+> to clone the first map into a new, empty, map, and then use `cxMapUnion()`.
 
 Refer to the documentation of the [clone-function callback](allocator.h.md#clone-function) to learn how to implement it.