From 409612297994996e82ca977db765958d466d1282 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Sat, 30 Sep 2017 15:02:03 +0200
Subject: [PATCH] add `CCMap.union`

---
 src/core/CCMap.ml  | 14 ++++++++++++++
 src/core/CCMap.mli |  5 +++++
 2 files changed, 19 insertions(+)

diff --git a/src/core/CCMap.ml b/src/core/CCMap.ml
index 056c01d2..1f2a5d55 100644
--- a/src/core/CCMap.ml
+++ b/src/core/CCMap.ml
@@ -29,6 +29,11 @@ module type S = sig
   (** [merge_safe ~f a b] merges the maps [a] and [b] together.
       @since 0.17 *)
 
+  val union : (key -> 'a -> 'a -> 'a option) -> 'a t -> 'a t -> 'a t
+  (** Union of both maps, using the function to combine bindings
+      that belong to both inputs
+      @since NEXT_RELEASE *)
+
   val of_seq : (key * 'a) sequence -> 'a t
 
   val add_seq : 'a t -> (key * 'a) sequence -> 'a t
@@ -85,6 +90,15 @@ module Make(O : Map.OrderedType) = struct
          | Some v1, Some v2 -> f k (`Both (v1,v2)))
       a b
 
+  let union f a b =
+    merge
+      (fun k v1 v2 -> match v1, v2 with
+         | None, None -> assert false
+         | None, (Some _ as r) -> r
+         | Some _ as r, None -> r
+         | Some v1, Some v2 -> f k v1 v2)
+      a b
+
   let add_seq m s =
     let m = ref m in
     s (fun (k,v) -> m := add k v !m);
diff --git a/src/core/CCMap.mli b/src/core/CCMap.mli
index 8ba47dd7..15e3c24a 100644
--- a/src/core/CCMap.mli
+++ b/src/core/CCMap.mli
@@ -32,6 +32,11 @@ module type S = sig
   (** [merge_safe ~f a b] merges the maps [a] and [b] together.
       @since 0.17 *)
 
+  val union : (key -> 'a -> 'a -> 'a option) -> 'a t -> 'a t -> 'a t
+  (** Union of both maps, using the function to combine bindings
+      that belong to both inputs
+      @since NEXT_RELEASE *)
+
   val of_seq : (key * 'a) sequence -> 'a t
   (** Same as {!of_list} *)