Implement contains_key and contains_key_alt

Implement functions to check if a key exists in the map

Author: vbrandl

src/lib.rs

@@ -149,6 +149,60 @@ impl<K1: Eq + Hash + Clone, K2: Eq + Hash + Clone, V> MultiMap<K1, K2, V> {
         result
     }
 
+    /// Returns true if the map contains a value for the specified key. The key may be any borrowed
+    /// form of the map's key type, but Hash and Eq on the borrowed form must match those for the
+    /// key type
+    ///
+    /// ## Example
+    /// ```
+    /// #[macro_use]
+    /// extern crate multi_map;
+    /// use multi_map::MultiMap;
+    /// # fn main() {
+    /// let map = multimap! {
+    ///     1, "One" => String::from("Eins"),
+    ///     2, "Two" => String::from("Zwei"),
+    ///     3, "Three" => String::from("Drei"),
+    /// };
+    /// assert!(map.contains_key(&1));
+    /// assert!(!map.contains_key(&4));
+    /// # }
+    /// ```
+    pub fn contains_key<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        K1: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.value_map.contains_key(key)
+    }
+
+    /// Returns true if the map contains a value for the specified alternative key. The key may be
+    /// any borrowed form of the map's key type, but Hash and Eq on the borrowed form must match
+    /// those for the key type
+    ///
+    /// ## Example
+    /// ```
+    /// #[macro_use]
+    /// extern crate multi_map;
+    /// use multi_map::MultiMap;
+    /// # fn main() {
+    /// let map = multimap! {
+    ///     1, "One" => String::from("Eins"),
+    ///     2, "Two" => String::from("Zwei"),
+    ///     3, "Three" => String::from("Drei"),
+    /// };
+    /// assert!(map.contains_key_alt(&"One"));
+    /// assert!(!map.contains_key_alt(&"Four"));
+    /// # }
+    /// ```
+    pub fn contains_key_alt<Q: ?Sized>(&self, key: &Q) -> bool
+    where
+        K2: Borrow<Q>,
+        Q: Hash + Eq,
+    {
+        self.key_map.contains_key(key)
+    }
+
     /// Remove an item from the HashMap using the secondary key. The value for
     /// the given key is returned (if it exists). Ordinary HashMaps can't do
     /// this. This removes an item from both the main HashMap and the second
@@ -251,6 +305,10 @@ mod test {
         assert!(*map.get(&1).unwrap() == String::from("Ein"));
         assert!(*map.get(&2).unwrap() == String::from("Zwei"));
         assert!(*map.get(&3).unwrap() == String::from("Drei"));
+        assert!(map.contains_key(&1));
+        assert!(!map.contains_key(&4));
+        assert!(map.contains_key_alt(&"One"));
+        assert!(!map.contains_key_alt(&"Four"));
 
         map.get_mut_alt(&"One").unwrap().push_str("s");