MultiHashMap: Provide the converse of `add_one`

Signed-off-by: Jean-Christophe Beaupré <jcbrinfo@users.noreply.github.com>

diff --git a/lib/more_collections.nit b/lib/more_collections.nit
index 2ea732a..81688d9 100644 (file)
--- a/lib/more_collections.nit
+++ b/lib/more_collections.nit
@@ -38,6 +38,8 @@ class MultiHashMap[K, V]
        #
        # If there is no array associated, then create it.
        #
+       # For the inverse operation, see `remove_one`.
+       #
        # ```
        # var m = new MultiHashMap[String, Char]
        # m.add_one("four", 'i')
@@ -62,6 +64,44 @@ class MultiHashMap[K, V]
                self[key] = res
                return res
        end
+
+       # Remove an occurrence of `v` from the array associated with `k`.
+       #
+       # If the associated array does not contain `v`, do nothing. If the
+       # associated array only contain one element and this element is `v`, remove
+       # the key `k`.
+       #
+       # In a nutshell, does the inverse operation of `add_one`.
+       #
+       # ```
+       # var m = new MultiHashMap[String, Char]
+       # m["four"]        =  ['4', 'i', 'i', 'i', 'i']
+       # m.remove_one("four", 'i')
+       # assert m["four"] == ['4', 'i', 'i', 'i']
+       #
+       # m = new MultiHashMap[String, Char]
+       # m.add_one("one", '1')
+       # m.remove_one("one", '?')
+       # assert m["one"] == ['1']
+       # m.remove_one("one", '1')
+       # assert not m.has_key("one")
+       # assert m["one"] == new Array[Char]
+       #
+       # m = new MultiHashMap[String, Char]
+       # m.add_one("one", '1')
+       # m.remove_one("two", '2')
+       # assert not m.has_key("two")
+       # assert m["one"] == ['1']
+       # assert m["two"] == new Array[Char]
+       # ```
+       fun remove_one(k: K, v: V)
+       do
+               var x = get_or_null(k)
+               if x != null then
+                       x.remove(v)
+                       if x.is_empty then keys.remove(k)
+               end
+       end
 end
 
 # Simple way to store an `HashMap[K1, HashMap[K2, V]]`