[cfe-users] compiler bug or language feature?

[Richard Smith]

On Tue, Oct 8, 2013 at 3:02 PM, Daniel Schwalbe <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>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>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
>>> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-users
>>>
>>>
>>
>>
>
>
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