From 39e403c1d2431f4adb801a5c210ac274be707a5f Mon Sep 17 00:00:00 2001
From: Jason Volk <jason@zemos.net>
Date: Sat, 19 May 2018 16:57:53 -0700
Subject: [PATCH] ircd::json: Add template to get tuple key string with runtime
 index.

---
 include/ircd/json/tuple/tuple.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/ircd/json/tuple/tuple.h b/include/ircd/json/tuple/tuple.h
index 6e1ecd680..d2e55d40a 100644
--- a/include/ircd/json/tuple/tuple.h
+++ b/include/ircd/json/tuple/tuple.h
@@ -126,6 +126,24 @@ key()
 	return tuple_element<tuple, i>::key;
 }
 
+template<class tuple,
+         size_t i>
+constexpr typename std::enable_if<i == tuple::size(), const char *>::type
+key(const size_t &j)
+{
+	return nullptr;
+}
+
+template<class tuple,
+         size_t i = 0>
+constexpr typename std::enable_if<i < tuple::size(), const char *>::type
+key(const size_t &j)
+{
+	return j == i?
+		tuple_element<tuple, i>::key:
+		key<tuple, i + 1>(j);
+}
+
 template<size_t i,
          class tuple>
 enable_if_tuple<tuple, const char *const &>