Fix PR19460 - std::ios is convertible to int.

std::basic_ios has an operator bool(). In C++11 and later
it is explicit, and only allows contextual implicit conversions.

However explicit isn't available in C++03 which causes std::istream (et al)
to have an implicit conversion to int. This can easily cause ambiguities
when calling operator<< and operator>>.

This patch uses a "bool-like" type in C++03 to work around this. The
"bool-like" type is an arbitrary pointer to member function type. It
will not convert to either int or void*, but will convert to bool.

llvm-svn: 290750

1 files changed, 7 insertions, 0 deletions

diff --git a/libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp b/libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
index 0de889e549c..5f49c65bdfd 100644
--- a/libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
+++ b/libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
@@ -14,6 +14,7 @@
 // operator unspecified-bool-type() const;
 
 #include <ios>
+#include <type_traits>
 #include <cassert>
 
 int main()
@@ -22,4 +23,10 @@ int main()
     assert(static_cast<bool>(ios) == !ios.fail());
     ios.setstate(std::ios::failbit);
     assert(static_cast<bool>(ios) == !ios.fail());
+    static_assert((!std::is_convertible<std::ios, void*>::value), "");
+    static_assert((!std::is_convertible<std::ios, int>::value), "");
+    static_assert((!std::is_convertible<std::ios const&, int>::value), "");
+#if TEST_STD_VER >= 11
+    static_assert((!std::is_convertible<std::ios, bool>::value), "");
+#endif
 }