From c528e28a0e34068469a6264009dca102e18a5a4f Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Mon, 16 Mar 2020 14:12:04 +1100
Subject: [PATCH] concepts: add "supports_indexing"

---
 concepts.hpp | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/concepts.hpp b/concepts.hpp
index 40b02fb7..785d922f 100644
--- a/concepts.hpp
+++ b/concepts.hpp
@@ -288,6 +288,13 @@ namespace cruft::concepts {
     };
 
 
+    template <
+        typename ContainerT,
+        typename IndexT = std::size_t
+    >
+    concept supports_indexing = requires (ContainerT &t, IndexT idx) {
+        { t[idx] };
+    };
 
 
     /// A type that supports arithmetic operators.