diff --git a/core/src/coordinates.rs b/core/src/coordinates.rs
index fd0d25e..7e4be53 100644
--- a/core/src/coordinates.rs
+++ b/core/src/coordinates.rs
@@ -90,6 +90,10 @@ macro_rules! range_bound_struct {
             $vis unsafe fn new_unchecked(x: $repr) -> Self {
                 Self(x)
             }
+
+            $vis fn as_index(&self) -> &$repr {
+                &self.0
+            }
         }
 
         impl Into<$repr> for $type {