[Bug c++/53972] New: array constant expression expression not valid as template argument

[fw at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53972

             Bug #: 53972
           Summary: array constant expression expression not valid as
                    template argument
    Classification: Unclassified
           Product: gcc
           Version: 4.8.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassig...@gcc.gnu.org
        ReportedBy: f...@gcc.gnu.org


Instantiating sub1 failes with:

bug.cc:10:24: error: ‘array’ is not a constant expression
   return Constify<array[I]>::value;

This is inconsistent because sub2 shows that the array subscript is recognized
as a constant expression in other context.

template <unsigned I>
struct Constify {
  enum { value = I };
};

template <unsigned N>
constexpr char
sub1(const char (&array)[N], unsigned I)
{
  return Constify<array[I]>::value;
}

template <unsigned N>
constexpr char
sub2(const char (&array)[N], unsigned I)
{
  return array[I];
}

int
main()
{
  sub1("foo", 2);
  enum {
    value = sub2("foo", 2)
  };
  Constify<value>::value;
}