From 9ce9a7ce9996b46737f569b56923fdef26e783f6 Mon Sep 17 00:00:00 2001
From: Peter Dimov <pdimov@gmail.com>
Date: Tue, 30 Jun 2020 21:58:58 +0300
Subject: [PATCH] Define protect(f)::result_type only when F::result_type is
 defined

---
 include/boost/bind/protect.hpp | 18 +++++++++++++++---
 test/protect_test2.cpp         | 20 ++++++++++++++++++++
 2 files changed, 35 insertions(+), 3 deletions(-)

diff --git a/include/boost/bind/protect.hpp b/include/boost/bind/protect.hpp
index d6a480d..e251129 100644
--- a/include/boost/bind/protect.hpp
+++ b/include/boost/bind/protect.hpp
@@ -24,7 +24,21 @@ namespace _bi
 
 #if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_RVALUE_REFERENCES) && !defined(BOOST_NO_CXX11_DECLTYPE)
 
-template<class F> class protected_bind_t
+template<class T> struct protect_make_void
+{
+    typedef void type;
+};
+
+template<class F, class E = void> struct protect_result_type
+{
+};
+
+template<class F> struct protect_result_type< F, typename protect_make_void<typename F::result_type>::type >
+{
+    typedef typename F::result_type result_type;
+};
+
+template<class F> class protected_bind_t: public protect_result_type<F>
 {
 private:
 
@@ -32,8 +46,6 @@ private:
 
 public:
 
-    typedef typename F::result_type result_type;
-
     explicit protected_bind_t( F f ): f_( f )
     {
     }
diff --git a/test/protect_test2.cpp b/test/protect_test2.cpp
index 66bec47..0c29500 100644
--- a/test/protect_test2.cpp
+++ b/test/protect_test2.cpp
@@ -18,9 +18,29 @@ struct X
     struct result_type {};
 };
 
+struct Y
+{
+};
+
+template<class T, class U> struct inherit: T, U
+{
+};
+
+template<class F> void test2( F )
+{
+    // test that F doesn't have ::result_type
+    BOOST_TEST_TRAIT_TRUE((boost::core::is_same<typename inherit<F, X>::result_type, typename X::result_type>));
+}
+
 int main()
 {
     test<X>( boost::protect( X() ) );
 
+#if !defined(BOOST_NO_CXX11_VARIADIC_TEMPLATES) && !defined(BOOST_NO_CXX11_RVALUE_REFERENCES) && !defined(BOOST_NO_CXX11_DECLTYPE)
+
+    test2( boost::protect( Y() ) );
+
+#endif
+
     return boost::report_errors();
 }