1 files changed, 33 insertions, 0 deletions
diff --git a/ecs/src/util.rs b/ecs/src/util.rs
index 0273b18..71021cd 100644
--- a/ecs/src/util.rs
+++ b/ecs/src/util.rs
@@ -1,5 +1,38 @@
+use std::hash::Hash;
 use std::ops::BitAnd;
 
+use hashbrown::HashMap;
+
+pub trait HashMapExt<Key, Value>
+{
+    /// Returns true if the keys are a subset of another [`HashMap`]'s keys, i.e., `other`
+    /// contains at least all the keys in `self`.
+    fn keys_is_subset(&self, other: &Self) -> bool;
+
+    /// Returns true if the keys are a superset of another [`HashMap`]'s keys, i.e.,
+    /// `self` contains at least all the keys in `other`.
+    fn keys_is_superset(&self, other: &Self) -> bool;
+}
+
+impl<Key, Value> HashMapExt<Key, Value> for HashMap<Key, Value>
+where
+    Key: Eq + Hash,
+{
+    fn keys_is_subset(&self, other: &Self) -> bool
+    {
+        if self.len() <= other.len() {
+            self.keys().all(|key| other.contains_key(key))
+        } else {
+            false
+        }
+    }
+
+    fn keys_is_superset(&self, other: &Self) -> bool
+    {
+        other.keys_is_subset(self)
+    }
+}
+
 pub trait Array<Item>:
     AsRef<[Item]>
     + AsMut<[Item]>