[libcxx-commits] [PATCH] D107663: [libc++] Restore `basic_ios`'s implicit conversion to `bool` in C++03 mode.

[Arthur O'Dwyer via Phabricator via libcxx-commits]

Quuxplusone updated this revision to Diff 365641.
Quuxplusone added a comment.

Welp, obviously that broke the existing test that tests `!std::is_convertible<std::istream&, void*>`.
So I propose we change the test, on the theory that "match libstdc++'s behavior exactly" is more important than "match libc++'s old behavior in some but not all obscure corner cases" (which is what I was trying to achieve with `operator const void*` in the original version of this PR). @ldionne, does this still seem reasonable to you?


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D107663/new/

https://reviews.llvm.org/D107663

Files:
  libcxx/include/ios
  libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp


Index: libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
===================================================================
--- libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
+++ libcxx/test/std/input.output/iostreams.base/ios/iostate.flags/bool.pass.cpp
@@ -24,10 +24,16 @@
     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), "");
-    static_assert((!std::is_convertible<std::ios, bool>::value), "");
+#if TEST_STD_VER >= 11
+    static_assert(!std::is_convertible<std::ios, void*>::value, "");
+    static_assert(!std::is_convertible<std::ios, bool>::value, "");
+#else
+    static_assert(std::is_convertible<std::ios, void*>::value, "");
+    static_assert(std::is_convertible<std::ios, bool>::value, "");
+    (void)(ios == 0);  // SPEC2006 apparently relies on this to compile
+#endif
 
   return 0;
 }
Index: libcxx/include/ios
===================================================================
--- libcxx/include/ios
+++ libcxx/include/ios
@@ -607,8 +607,15 @@
     static_assert((is_same<_CharT, typename traits_type::char_type>::value),
                   "traits_type::char_type must be the same type as CharT");
 
+#ifdef _LIBCPP_CXX03_LANG
+    // Preserve the ability to compare with literal 0,
+    // and implicitly convert to bool, but not implicitly convert to int.
+    _LIBCPP_INLINE_VISIBILITY
+    operator void*() const {return fail() ? nullptr : (void*)this;}
+#else
     _LIBCPP_INLINE_VISIBILITY
     explicit operator bool() const {return !fail();}
+#endif
 
     _LIBCPP_INLINE_VISIBILITY bool operator!() const    {return  fail();}
     _LIBCPP_INLINE_VISIBILITY iostate rdstate() const   {return ios_base::rdstate();}


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