[Bug c++/64519] New: variadic template as the first argument

["roman.kurc at wp dot pl" <gcc-bugzilla@gcc.gnu.org>]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=64519

            Bug ID: 64519
           Summary: variadic template as the first argument
           Product: gcc
           Version: 4.9.2
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: roman.kurc at wp dot pl

Created attachment 34392
  --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=34392&action=edit
sample code

It seems that passing an empty argument to a variadic template results in
assigning void type to the argument.


Such a behavior can be seen in the following cases:

static_assert( std::is_same< decltype(B::test()), B::CharA<3> >::value ==
false, "test( ) should evaluate to fun( )" );

test( TA... args ) is called with no parameters then I<TA...>::template
sfinae_2<B>(args...,0) and args... gets void type. 

The same happens in calls presented below and it does not matter if template is
instantinated or only its type is deduced.


static_assert( (sizeof(B::test()) == sizeof(B::CharA<1>)), "test( ) should
evaluate to fun ()" );

static_assert( std::is_same< decltype(B::test()), B::CharA<1> >::value, "test()
should evaluate to fun()" );