diff --git a/maths.hpp b/maths.hpp
index 8566c660..a83a7753 100644
--- a/maths.hpp
+++ b/maths.hpp
@@ -139,6 +139,15 @@ constexpr float sign (float);
 constexpr double sign (double);
 
 
+//-----------------------------------------------------------------------------
+template <typename T>
+const T&
+identity (const T& t)
+{
+    return t;
+}
+
+
 //-----------------------------------------------------------------------------
 // Comparisons
 template <typename T>