From 69acdf6584be2a04094e27b395c50c071b2b15cf Mon Sep 17 00:00:00 2001
From: Dan Goodliffe <dan@randomdan.homeip.net>
Date: Wed, 28 Dec 2022 13:49:54 +0000
Subject: Use the existence of .substr(...) to test if a T is stringlike

---
 lib/stream_support.hpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

(limited to 'lib/stream_support.hpp')

diff --git a/lib/stream_support.hpp b/lib/stream_support.hpp
index 5f45cbf..a3565d8 100644
--- a/lib/stream_support.hpp
+++ b/lib/stream_support.hpp
@@ -8,14 +8,16 @@
 #include <sstream>
 #include <type_traits>
 
+template<typename S>
+concept stringlike = requires(const S & s) { s.substr(0); };
 template<typename T>
 concept spanable = std::is_constructible_v<std::span<const typename T::value_type>, T> && !
-std::is_same_v<char, std::decay_t<typename T::value_type>>;
+stringlike<T> && !std::is_same_v<std::span<typename T::value_type>, T>;
 
 namespace std {
 	template<typename T, std::size_t L>
 	std::ostream &
-	operator<<(std::ostream & s, const span<const T, L> v)
+	operator<<(std::ostream & s, const span<T, L> v)
 	{
 		s << '(';
 		for (const auto & i : v) {
-- 
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