lib: add `MapRead::get_or_null` to provide a more standard usage of Maps

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 b178386..c86c748 100644 (file)
--- a/lib/standard/collection/abstract_collection.nit
+++ b/lib/standard/collection/abstract_collection.nit
@@ -280,6 +280,20 @@ interface MapRead[K: Object, E]
        # Get the item at `key`.
        fun [](key: K): E is abstract
 
+       # Get the item at `key` or null if `key` is not in the map.
+       #
+       #     var x = new HashMap[String, Int]
+       #     x["four"] = 4
+       #     assert x.get_or_null("four") == 4
+       #     assert x.get_or_null("five") == null
+       #
+       # Note: use `has_key` and `[]` if you need the distinction bewteen a key associated with null, and no key.
+       fun get_or_null(key: K): nullable E
+       do
+               if has_key(key) then return self[key]
+               return null
+       end
+
        # Get the item at `key` or return `default` if not in map
        fun get_or_default(key: K, default: E): E
        do