From e61a86bbb25f9e0943387738f1e138743c8fe166 Mon Sep 17 00:00:00 2001
From: Gleb Natapov <gleb@scylladb.com>
Date: Thu, 29 Aug 2019 13:09:02 +0300
Subject: [PATCH] to_string: Add operator<< overload for std::tuple.

Message-Id: <20190829100902.GN21540@scylladb.com>
---
 to_string.hh | 24 ++++++++++++++++++++++++
 1 file changed, 24 insertions(+)

diff --git a/to_string.hh b/to_string.hh
index 6295144827..a17ef63cac 100644
--- a/to_string.hh
+++ b/to_string.hh
@@ -51,6 +51,20 @@ sstring join(sstring delimiter, const PrintableRange& items) {
     return join(delimiter, items.begin(), items.end());
 }
 
+template<bool NeedsComma, typename Printable>
+struct print_with_comma {
+    const Printable& v;
+};
+
+template<bool NeedsComma, typename Printable>
+std::ostream& operator<<(std::ostream& os, const print_with_comma<NeedsComma, Printable>& x) {
+    os << x.v;
+    if (NeedsComma) {
+        os << ", ";
+    }
+    return os;
+}
+
 namespace std {
 
 template<typename Printable>
@@ -87,6 +101,16 @@ std::ostream& operator<<(std::ostream& os, const std::pair<K, V>& p) {
     return os;
 }
 
+template<typename... T, size_t... I>
+std::ostream& print_tuple(std::ostream& os, const std::tuple<T...>& p, std::index_sequence<I...>) {
+    return ((os << "{" ) << ... << print_with_comma<I < sizeof...(I) - 1, T>{std::get<I>(p)}) << "}";
+}
+
+template <typename... T>
+std::ostream& operator<<(std::ostream& os, const std::tuple<T...>& p) {
+    return print_tuple(os, p, std::make_index_sequence<sizeof...(T)>());
+}
+
 template <typename T>
 std::ostream& operator<<(std::ostream& os, const std::unordered_set<T>& items) {
     os << "{" << join(", ", items) << "}";