[Bug c++/79832] New: [C++14/17] result of array subscript operator should be xvlaue

[felix.morgner at gmail dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79832

            Bug ID: 79832
           Summary: [C++14/17] result of array subscript operator should
                    be xvlaue
           Product: gcc
           Version: 6.3.1
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
          Assignee: unassigned at gcc dot gnu.org
          Reporter: felix.morgner at gmail dot com
  Target Milestone: ---

According to ISO14882:2014 [expr.sub] (as well as the current draft) the
following should yield an xvalue on line 3 (arr{}[0]):

  int main() {
    using arr = int[3];
    arr{}[0];
  }

since 'arr{}' is an array prvalue. It seems that it does not in GCC since the
following code compiles just fine:

  int main() {
    using arr = int[3];
    &arr{}[0];
  }

even though taking the address of an xvalue (the result of subscripting the
array prvalue) is invalid. There exists a relevant DR1213 (pre C++14) here:
http://www.open-std.org/jtc1/sc22/wg21/docs/cwg_defects.html#1213 which
introduced the notion that subscripting a non lvalue array yields an xvalue.

Compiled using -Wall -Wextra -pedantic with GCC 6.3.1