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Eliminate the C++0x-only is_convertible testing function that accepts

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a cv-qualifier rvalue reference to the type, e.g.,

  template <class _Tp> char  __test(const volatile typename remove_reference<_Tp>::type&&);

The use of this function signature rather than the more
straightforward one used in C++98/03 mode, e.g.,

  template <class _Tp> char  __test(_Tp);

is broken in two ways:

  1) An rvalue reference cannot bind to lvalues, so is_convertible<X&,
  X&>::value would be false. This breaks two of the unique_ptr tests
  on Clang and GCC >= 4.5. Prior GCC's seem to have allowed rvalue
  references to bind to lvalues, allowing this bug to slip in.

  2) By adding cv-qualifiers to the type we're converting to, we get
  some incorrect "true" results for, e.g., is_convertible<const X&, X&>::value.





git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@124166 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Douglas Gregor 2011-01-25 01:15:41 +00:00
parent f83417b823
commit f9e1c7e367
2 changed files with 15 additions and 4 deletions
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4
include/type_traits
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@ -600,11 +600,7 @@ template <class _Tp> struct _LIBCPP_VISIBLE is_abstract : public __libcpp_abstra
namespace __is_convertible_imp namespace __is_convertible_imp
{ {
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
template <class _Tp> char __test(const volatile typename remove_reference<_Tp>::type&&);
#else
template <class _Tp> char __test(_Tp); template <class _Tp> char __test(_Tp);
#endif
template <class _Tp> __two __test(...); template <class _Tp> __two __test(...);
#ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
template <class _Tp> _Tp&& __source(); template <class _Tp> _Tp&& __source();

15
test/utilities/meta/meta.rel/is_convertible.pass.cpp
View File

@ -16,6 +16,10 @@
typedef void Function(); typedef void Function();
typedef char Array[1]; typedef char Array[1];
class NonCopyable {
NonCopyable(NonCopyable&);
};
int main() int main()
{ {
{ {
@ -366,4 +370,15 @@ int main()
static_assert((!std::is_convertible<const char*, char*>::value), ""); static_assert((!std::is_convertible<const char*, char*>::value), "");
static_assert(( std::is_convertible<const char*, const char*>::value), ""); static_assert(( std::is_convertible<const char*, const char*>::value), "");
} }
{
static_assert((std::is_convertible<NonCopyable&, NonCopyable&>::value), "");
static_assert((std::is_convertible<NonCopyable&, const NonCopyable&>::value), "");
static_assert((std::is_convertible<NonCopyable&, const volatile NonCopyable&>::value), "");
static_assert((std::is_convertible<NonCopyable&, volatile NonCopyable&>::value), "");
static_assert((std::is_convertible<const NonCopyable&, const NonCopyable&>::value), "");
static_assert((std::is_convertible<const NonCopyable&, const volatile NonCopyable&>::value), "");
static_assert((std::is_convertible<volatile NonCopyable&, const volatile NonCopyable&>::value), "");
static_assert((std::is_convertible<const volatile NonCopyable&, const volatile NonCopyable&>::value), "");
static_assert((!std::is_convertible<const NonCopyable&, NonCopyable&>::value), "");
}
} }