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
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 2131a71c0525c556b73441dc905e3956e8e54f70
diff --git a/include/ios b/include/ios
index cbea478..dfeb1f6 100644
--- a/include/ios
+++ b/include/ios
@@ -585,9 +585,22 @@
typedef typename traits_type::pos_type pos_type;
typedef typename traits_type::off_type off_type;
+#if defined(_LIBCPP_CXX03_LANG)
+private:
+ struct __bool_tag {};
+ typedef void (basic_ios::*_BoolType)(__bool_tag) const;
+ void __true_value(__bool_tag) const {}
+
+public:
_LIBCPP_ALWAYS_INLINE
- _LIBCPP_EXPLICIT
- operator bool() const {return !fail();}
+ operator _BoolType() const {
+ return !fail() ? &basic_ios::__true_value : nullptr;
+ }
+#else
+ _LIBCPP_ALWAYS_INLINE
+ _LIBCPP_EXPLICIT operator bool() const {return !fail();}
+#endif
+
_LIBCPP_ALWAYS_INLINE bool operator!() const {return fail();}
_LIBCPP_ALWAYS_INLINE iostate rdstate() const {return ios_base::rdstate();}
_LIBCPP_ALWAYS_INLINE void clear(iostate __state = goodbit) {ios_base::clear(__state);}