[Bug libstdc++/33490] New: parallel v3: std::accumulate assumes iterators have std::iterator_traits declared

[bangerth at dealii dot org]

The parallel version of std::accumulate assumes that iterator_traits
are declared for the iterator arguments. However, the standard only
requires them to be of kind InputIterator, and the table that describes
what types of this kind have to satisfy does not include the necessity
to declare a specialization of std::iterator_traits.

Example in point: this doesn't compile with current parallel v3:
--------------------
#include <numeric>

struct X {
    int operator* () const;
    bool operator != (const X&) const;
    X operator ++ ();
};

void f () {
  X p, q;
  std::accumulate (p, q, 0);
}
---------------------

4.3.0/bits/stl_iterator_base_types.h: In instantiation of
'std::iterator_traits<X>':
4.3.0/parallel/numeric:83:   instantiated from 'T
std::__parallel::accumulate(_IIter, _IIter, T, __gnu_parallel::parallelism)
[with _IIter = X, T = int]'
x.cc:11:   instantiated from here
4.3.0/bits/stl_iterator_base_types.h:133: error: no type named
'iterator_category' in 'struct X'
4.3.0/bits/stl_iterator_base_types.h:134: error: no type named 'value_type' in
'struct X'
4.3.0/bits/stl_iterator_base_types.h:135: error: no type named
'difference_type' in 'struct X'
4.3.0/bits/stl_iterator_base_types.h:136: error: no type named 'pointer' in
'struct X'
4.3.0/bits/stl_iterator_base_types.h:137: error: no type named 'reference' in
'struct X'


-- 
           Summary: parallel v3: std::accumulate assumes iterators have
                    std::iterator_traits declared
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Keywords: rejects-valid
          Severity: normal
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: bangerth at dealii dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33490