[cfe-commits] [libcxx] r124166 - in /libcxx/trunk: include/type_traits test/utilities/meta/meta.rel/is_convertible.pass.cpp

[Howard Hinnant]

Thanks Doug.

Ultimately I'd like to see is_convertible mapped into a compiler intrinsic.

-Howard

On Jan 24, 2011, at 8:15 PM, Douglas Gregor wrote:

> Author: dgregor
> Date: Mon Jan 24 19:15:41 2011
> New Revision: 124166
> 
> URL: http://llvm.org/viewvc/llvm-project?rev=124166&view=rev
> Log:
> Eliminate the C++0x-only is_convertible testing function that accepts
> 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.
> 
> 
> 
> 
> Modified:
>    libcxx/trunk/include/type_traits
>    libcxx/trunk/test/utilities/meta/meta.rel/is_convertible.pass.cpp
> 
> Modified: libcxx/trunk/include/type_traits
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/include/type_traits?rev=124166&r1=124165&r2=124166&view=diff
> ==============================================================================
> --- libcxx/trunk/include/type_traits (original)
> +++ libcxx/trunk/include/type_traits Mon Jan 24 19:15:41 2011
> @@ -600,11 +600,7 @@
> 
> 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);
> -#endif
> template <class _Tp> __two __test(...);
> #ifndef _LIBCPP_HAS_NO_RVALUE_REFERENCES
> template <class _Tp> _Tp&& __source();
> 
> Modified: libcxx/trunk/test/utilities/meta/meta.rel/is_convertible.pass.cpp
> URL: http://llvm.org/viewvc/llvm-project/libcxx/trunk/test/utilities/meta/meta.rel/is_convertible.pass.cpp?rev=124166&r1=124165&r2=124166&view=diff
> ==============================================================================
> --- libcxx/trunk/test/utilities/meta/meta.rel/is_convertible.pass.cpp (original)
> +++ libcxx/trunk/test/utilities/meta/meta.rel/is_convertible.pass.cpp Mon Jan 24 19:15:41 2011
> @@ -16,6 +16,10 @@
> typedef void Function();
> typedef char Array[1];
> 
> +class NonCopyable {
> +  NonCopyable(NonCopyable&);
> +};
> +
> int main()
> {
>     {
> @@ -366,4 +370,15 @@
>     static_assert((!std::is_convertible<const char*, 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), "");
> +    }
> }
> 
> 
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits