[cfe-users] compiler bug or language feature?

[Daniel Schwalbe]

Thank you all for your help. I filed now a bug report ( 
http://llvm.org/bugs/show_bug.cgi?id=17528) for this issue.

Am 09.10.2013 18:50, schrieb Richard Smith:
> On Tue, Oct 8, 2013 at 3:02 PM, Daniel Schwalbe <dansch491 at gmail.com 
> <mailto:dansch491 at gmail.com>> wrote:
>
>     Hmm, if I do this it gives me another error:
>
>     test.cpp:15:42: error: 'SmartPtrType' following the 'template'
>     keyword does not refer to a template
>      ~SmartUnion() {m_sptr.SmartPtrType<T>::~SmartPtrType<T>(); }
>
>
> This is a bug. (Also, there's no 'template' keyword here, so the 
> diagnostic is simultaneously wrong in two different ways.)
>
>     Again, g++ takes it without complaining.
>
>     Since I noticed that my original attachment got scrubbed I am
>     pasting the modified test program directly. Perhaps the context
>     will help to sort things out:
>
>
> Thanks, this helped.
>
>     #include <memory>
>     #include <string>
>     using namespace std;
>
>     //comment this in to see the compiler error
>     #define show_compiler_error 1
>
>     template<typename T, template<class> class SmartPtrType = shared_ptr>
>     struct SmartUnion
>     {
>         SmartUnion() {new(&m_sptr) SmartPtrType<T>();}
>
>
>     #ifdef show_compiler_error
>      ~SmartUnion() {m_sptr.SmartPtrType<T>::~SmartPtrType<T>(); }
>     #else
>      typedef SmartPtrType<T> smartptr_type;
>       ~SmartUnion() {m_sptr.smartptr_type::~smartptr_type(); }
>     #endif
>
>      union {
>          SmartPtrType<T> m_sptr;
>          T * m_ptr;
>      };
>
>     };
>
>     using namespace std;
>     int main()
>     {
>         SmartUnion<string,shared_ptr> smu;
>
>         return 0;
>     }
>
>
>     Am 08.10.2013 20:08, schrieb Richard Smith:
>>     You need to write
>>
>>     m_sptr.SmartPtrType<T>::~SmartPtrType*<T>*();
>>
>>     Per 3.4.3/6, "in a qualified-id of the form
>>     nested-name-specifier[opt] class-name::~class-name, the second
>>     class-name is looked up in the same scope as the first". So you
>>     can't use the injected-class-name after the ~, because it's not
>>     visible.
>>
>>     On Tue, Oct 8, 2013 at 10:05 AM, Daniel Schwalbe
>>     <dansch491 at gmail.com <mailto:dansch491 at gmail.com>> wrote:
>>
>>         When I add the 'template' keyword as suggested clang gives me
>>         the very same error. g++ still eats it without problem.
>>
>>         Am 08.10.2013 18:23, schrieb David Blaikie:
>>>
>>>
>>>
>>>         On Tue, Oct 8, 2013 at 8:36 AM, Daniel Schwalbe
>>>         <dansch491 at gmail.com <mailto:dansch491 at gmail.com>> wrote:
>>>
>>>             Hi,
>>>
>>>             I don't know if I encountered a compiler bug in clang
>>>             3.3 or if this is one of the many subtle c++ exceptional
>>>             cases:
>>>
>>>             When I try to compile the attached file (using: clang++
>>>             -std=c++11 test.cpp) I receive a compiler error:
>>>
>>>             "test.cpp:15:42: error: identifier 'SmartPtrType' in
>>>             object destruction expression does not name a type
>>>              ~SmartUnion() {m_sptr.SmartPtrType<T>::~SmartPtrType(); }"
>>>
>>>             g++ compiles the file without problem.
>>>
>>>             clang compiles it, too, if I explicitly introduce a
>>>             typedef for SmartPtrType<T> and call this typedef name
>>>             instead:
>>>
>>>             typedef SmartPtrType<T> smartptr_type;
>>>             ~SmartUnion() {m_sptr.smartptr_type::~smartptr_type(); }
>>>
>>>             Is this a subtle language feature or a compiler bug?
>>>
>>>
>>>         I believe this is a language feature because the expression
>>>         is ambiguous if m_sptr is type dependent (which I assume it is)
>>>
>>>         The other solution, rather than introducing a typedef, is to
>>>         use the 'template' keyword:
>>>
>>>         ~SmartUnion() {m_sptr.template
>>>         SmartPtrType<T>::~SmartPtrType(); }
>>>
>>>
>>>
>>>             Daniel
>>>
>>>
>>>
>>>
>>>             _______________________________________________
>>>             cfe-users mailing list
>>>             cfe-users at cs.uiuc.edu <mailto:cfe-users at cs.uiuc.edu>
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>>>
>>>
>>
>>
>
>

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