Bug in c++11 mode when instantiating template with local class

Edward Diener eldlistmailingz@tropicsoft.com
Thu Jun 22 16:42:00 GMT 2017


The code below asserts when being compiled with gcc in c++11 mode:

----------------------------------------------------------------------

#include <cassert>

typedef char yes_type;
struct no_type
{
    char padding[8];
};

template
     <
     class enclosing_type,
     class static_type
     >
struct has_static_member_function_StaticFunction
     {
     template<static_type *> struct helper;
     template<class internal_enclosing_type> static yes_type 
chkt(helper<&internal_enclosing_type::StaticFunction> *);
     template<class internal_enclosing_type> static no_type chkt(...);
     static const bool 
value=(sizeof(chkt<enclosing_type>(0))==sizeof(yes_type));
     };


     class AClass
     {
     public:
         static void StaticFunction()
         {
         }
     };

int main()
{
     class ANestedClass
     {
     public:
         static void StaticFunction()
         {
         }
     };

     assert((has_static_member_function_StaticFunction<ANestedClass,void 
()>::value));

     return 0;
}

-------------------------------------------------------------------------

If the 'assert" line instead is:

assert((has_static_member_function_StaticFunction<AClass,void ()>::value));

the assert does not occur. In other words the class template's 'value' 
is false when passing the local class and true when passing the 
non-local class.

The code is a simplified version of my Boost tti's library code for 
checking if a static member function of a given name exists within a class.

Is this a gcc bug or is my code wrong for local classes in c++11 mode, 
as opposed to non-local classes ?

I am fully aware that instantiating a template with a local class type 
is forbidden prior to c++11.

The compile and link lines, for gcc 7.1 as an example, are:

somepath/g++ -ftemplate-depth-128 -Wno-unused-local-typedefs 
-ftrack-macro-expansion=0 -Wno-unused-variable -std=c++11 -O0 
-fno-inline -Wall -pedantic -g -march=i686 -m32 -c -o somepath/example.o 
example.cpp

somepath/g++ -o example.exe -Wl,--start-group somepath/example.o 
-Wl,-Bstatic  -Wl,-Bdynamic  -Wl,--end-group -g -march=i686 -m32

If this is a bug in gcc I will be happy to report it on the bug tracker 
if it has not already been reported.







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