[Bug libstdc++/49022] [C++0x][DR 2058] std::begin and std::end specialized for std::valarray with some operators are missing.

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49022

--- Comment #18 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-06-14 12:51:45 UTC ---
(In reply to comment #16)
> Then, the snippet:
> 
>   std::valarray<int> v1{ 0, 1, 2, 3, 4 }, v2{ 5, 6, 7, 8, 9};
> 
>   for (int i : v1 + v2)
>     { std::cout << i << std::endl; } 
> 
> compiles but then misbehaves at compile-time, per valgrind too: apparently we
> don't have a proper range. Note that the following misbehaves exactly in the
> *same way*, and this appears to support my conjecture that we have a problem
> somewhere with two different temporary _Expr passed to the begin and end
> overloads:
> 
>   for (auto b = std::begin(v1 + v2), e = std::end(v1 + v2); b < e; ++b)
>     { std::cout << *b << std::endl; }

Hmm, then range-based for is implemented incorrectly, I'll take a look.
It should be identical to

auto&& range = v1 + v2;
for (auto b = std::begin(range), e = std::end(range); b != e; ++b)
  { ... }
(see 6.5.4 [stmt.ranged])

of course the same problem is present for any temporary expression:
std::string s = "hello"
  for (auto b = std::begin(s+"!"), e = std::end(s+"!"); b != e; ++b)
but it should work correctly as:
  for (auto c : s+"!")