From f2e1db8021ac03bde88028a95b99581922bb664f Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 26 Jul 2022 21:49:13 +0300
Subject: [PATCH] Constrain explicit value and error constructors to not accept
 zero arguments. Fixes #86.

---
 include/boost/system/result.hpp | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/include/boost/system/result.hpp b/include/boost/system/result.hpp
index 8ff55fb..4e6c00c 100644
--- a/include/boost/system/result.hpp
+++ b/include/boost/system/result.hpp
@@ -135,7 +135,8 @@ public:
     template<class... A, class En = typename std::enable_if<
         std::is_constructible<T, A...>::value &&
         !(detail::is_errc_t<A...>::value && std::is_arithmetic<T>::value) &&
-        !std::is_constructible<E, A...>::value
+        !std::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
         noexcept( std::is_nothrow_constructible<T, A...>::value )
@@ -146,7 +147,8 @@ public:
     // explicit, error
     template<class... A, class En2 = void, class En = typename std::enable_if<
         !std::is_constructible<T, A...>::value &&
-        std::is_constructible<E, A...>::value
+        std::is_constructible<E, A...>::value &&
+        sizeof...(A) >= 1
         >::type>
     explicit constexpr result( A&&... a )
         noexcept( std::is_nothrow_constructible<E, A...>::value )