2 files changed, 29 insertions, 0 deletions
diff --git a/macros/src/util/iterator_ext.rs b/macros/src/util/iterator_ext.rs
new file mode 100644
index 0000000..86db6cb
--- /dev/null
+++ b/macros/src/util/iterator_ext.rs
@@ -0,0 +1,28 @@
+use std::collections::HashMap;
+use std::hash::Hash;
+
+pub trait IteratorExt<Item>
+{
+    fn find_duplicate(&mut self) -> Option<Item>;
+}
+
+impl<Iter> IteratorExt<Iter::Item> for Iter
+where
+    Iter: Iterator,
+    Iter::Item: Eq + Hash + Copy,
+{
+    fn find_duplicate(&mut self) -> Option<Iter::Item>
+    {
+        let mut iterated_item_map = HashMap::<Iter::Item, ()>::new();
+
+        for item in self {
+            if iterated_item_map.contains_key(&item) {
+                return Some(item);
+            }
+
+            iterated_item_map.insert(item, ());
+        }
+
+        None
+    }
+}
diff --git a/macros/src/util/mod.rs b/macros/src/util/mod.rs
new file mode 100644
index 0000000..fe2fbbc
--- /dev/null
+++ b/macros/src/util/mod.rs
@@ -0,0 +1 @@
+pub mod iterator_ext;