From 9ac7984f74d6267affe43257237598e00e6503d7 Mon Sep 17 00:00:00 2001
From: Simon Cruanes <simon.cruanes.2007@m4x.org>
Date: Fri, 15 Dec 2017 13:49:34 +0100
Subject: [PATCH] add `Hash.const0` for trivial hash function that ignores its
 input

---
 src/core/CCHash.ml  | 1 +
 src/core/CCHash.mli | 6 ++++++
 2 files changed, 7 insertions(+)

diff --git a/src/core/CCHash.ml b/src/core/CCHash.ml
index c4741cf4..8b0b9ac7 100644
--- a/src/core/CCHash.ml
+++ b/src/core/CCHash.ml
@@ -24,6 +24,7 @@ let combine4 a b c d =
 (** {2 Combinators} *)
 
 let const h _ = h
+let const0 _ = 0
 
 let int i = i land max_int
 let bool b = if b then 1 else 2
diff --git a/src/core/CCHash.mli b/src/core/CCHash.mli
index 28c5fc54..e370934b 100644
--- a/src/core/CCHash.mli
+++ b/src/core/CCHash.mli
@@ -14,6 +14,12 @@ type 'a t = 'a -> hash
 val const : hash -> _ t
 (** [return h] hashes any value into [h]. Use with caution!. *)
 
+val const0 : _ t
+(** Always return 0. Useful for ignoring elements.
+    Example: [Hash.(pair string const0)] will map pairs [("a", 1)]
+    and [("a", 2)] to the same hash, but not the same as [("b", 1)]
+    @since NEXT_RELEASE *)
+
 val int : int t
 val bool : bool t
 val char : char t