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

[Douglas Gregor]

On Jan 24, 2011, at 6:07 PM, Howard Hinnant wrote:

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

Yeah, I agree that that would make sense. But, not until we've knocked off a few more C++0x features that libc++ needs!

  - Doug

> -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), "");
>> +    }
>> }
>> 
>> 
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> 

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