diff --git a/src/helper.rs b/src/helper.rs
index 2c91f75..44cc143 100644
--- a/src/helper.rs
+++ b/src/helper.rs
@@ -1,4 +1,30 @@
+/** Given an array of arguments, return them sorted.
+Best utilised with array destructuring. */
 pub fn ordered<T: Ord, const N: usize>(mut xs: [T; N]) -> [T; N] {
     xs.sort();
     xs
 }
+
+/** An iterator adaptor (derived from ExactSizedIterator) which has a guaranteed
+compile time size, allowing for collection of an iterator into a stack allocated
+array.  */
+pub trait ExactSizedArr<I>: ExactSizeIterator<Item = I> + Sized
+where
+    I: Default,
+{
+    fn into_array<const N: usize>(mut self) -> Result<[Self::Item; N], Self> {
+        if self.len() < N {
+            Err(self)
+        } else {
+            Ok(std::array::from_fn(|_| self.next().unwrap()))
+        }
+    }
+}
+
+/** Default implementation of ExactSizedArr for any ExactSizeIterator.  */
+impl<T, I> ExactSizedArr<T> for I
+where
+    T: Default + Copy + Clone,
+    I: ExactSizeIterator<Item = T>,
+{
+}