lib/standard: forgot to provide `Map::hash` when `Map::==` was implemented

Signed-off-by: Jean Privat <jean@pryen.org>

diff --git a/lib/standard/collection/abstract_collection.nit b/lib/standard/collection/abstract_collection.nit
index d38e001..1515ffd 100644 (file)
--- a/lib/standard/collection/abstract_collection.nit
+++ b/lib/standard/collection/abstract_collection.nit
@@ -497,6 +497,25 @@ interface MapRead[K, V]
                end
                return true
        end
+
+       # A hashcode based on the hashcode of the keys and the values.
+       #
+       # ~~~
+       # var a = new HashMap[String, Int]
+       # var b = new ArrayMap[Object, Numeric]
+       # a["one"] = 1
+       # b["one"] = 1
+       # assert a.hash == b.hash
+       # ~~~
+       redef fun hash
+       do
+               var res = length
+               for k, v in self do
+                       if k != null then res += k.hash * 7
+                       if v != null then res += v.hash * 11
+               end
+               return res
+       end
 end
 
 # Maps are associative collections: `key` -> `item`.