add CCRef.{get_then_incr,incr_then_get} functions

src/core/CCRef.ml

@@ -21,6 +21,14 @@ let iter f r = f !r
 
 let update f r = r := (f !r)
 
+let incr_then_get r =
+  incr r; !r
+
+let get_then_incr r =
+  let x = !r in
+  incr r;
+  x
+
 let compare f r1 r2 = f !r1 !r2
 
 let equal f r1 r2 = f !r1 !r2

src/core/CCRef.mli

@@ -24,6 +24,14 @@ val iter : ('a -> unit) -> 'a t -> unit
 val update : ('a -> 'a) -> 'a t -> unit
 (** Update the reference's content with the given function *)
 
+val incr_then_get : int t -> int
+(** [incr_then_get r] increments [r] and returns its new value, think [++ r]
+    @since NEXT_RELEASE *)
+
+val get_then_incr : int t -> int
+(** [get_then_incr r] increments [r] and returns its old value, think [r++]
+    @since NEXT_RELEASE *)
+
 val compare : 'a ord -> 'a t ord
 
 val equal : 'a eq -> 'a t eq