On Tue, 4 Feb 2020, Jonathan Wakely wrote:
> On 03/02/20 21:07 -0500, Patrick Palka wrote:
> > These changes are needed for some of the tests in the constrained algorithm
> > patch, because they use move_iterator with an uncopyable output_iterator.
> > The
> > other changes described in the paper are already applied, it seems.
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/stl_iterator.h (move_iterator::move_iterator): Move the
> > iterator when initializing _M_current.
> > (move_iterator::base): Split into two overloads differing in
> > ref-qualifiers as in P1207R4.
> > ---
> > libstdc++-v3/include/bits/stl_iterator.h | 11 +++++++++--
> > 1 file changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/libstdc++-v3/include/bits/stl_iterator.h
> > b/libstdc++-v3/include/bits/stl_iterator.h
> > index 784d200d22f..1a288a5c785 100644
> > --- a/libstdc++-v3/include/bits/stl_iterator.h
> > +++ b/libstdc++-v3/include/bits/stl_iterator.h
> > @@ -1166,7 +1166,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> >
> > explicit _GLIBCXX17_CONSTEXPR
> > move_iterator(iterator_type __i)
> > - : _M_current(__i) { }
> > + : _M_current(std::move(__i)) { }
> >
> > template<typename _Iter>
> > _GLIBCXX17_CONSTEXPR
> > @@ -1174,9 +1174,16 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> > : _M_current(__i.base()) { }
> >
> > _GLIBCXX17_CONSTEXPR iterator_type
> > - base() const
> > + base() const &
> > +#if __cplusplus > 201703L && __cpp_lib_concepts
> > + requires copy_constructible<iterator_type>
> > +#endif
> > { return _M_current; }
> >
> > + _GLIBCXX17_CONSTEXPR iterator_type
> > + base() &&
> > + { return std::move(_M_current); }
> > +
>
> I think this change has to be restricted to C++20 and later, otherwise
> a move_iterator in C++17 can change state so that its _M_current
> becomes moved-from, which should not be possible before C++20.
>
> So something like:
>
> #if __cplusplus <= 201703L
> _GLIBCXX17_CONSTEXPR iterator_type
> base() const
> { return _M_current; }
> #else
> constexpr iterator_type
> base() const &
> #if __cpp_lib_concepts
> requires copy_constructible<iterator_type>
> #endif
> { return _M_current; }
>
> constexpr iterator_type
> base() &&
> { return std::move(_M_current); }
> #endif
>
>
Thanks for the review, here is the updated patch.
libstdc++-v3/ChangeLog:
* include/bits/stl_iterator.h (move_iterator::move_iterator): Move __i
when initializing _M_current.
(move_iterator::base): Split into two overloads differing in
ref-qualifiers as in P1207R4 for C++20.
---
libstdc++-v3/include/bits/stl_iterator.h | 15 ++++++++++++++-
1 file changed, 14 insertions(+), 1 deletion(-)
diff --git a/libstdc++-v3/include/bits/stl_iterator.h
b/libstdc++-v3/include/bits/stl_iterator.h
index 784d200d22f..c200f7a9d14 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1166,16 +1166,29 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
explicit _GLIBCXX17_CONSTEXPR
move_iterator(iterator_type __i)
- : _M_current(__i) { }
+ : _M_current(std::move(__i)) { }
template<typename _Iter>
_GLIBCXX17_CONSTEXPR
move_iterator(const move_iterator<_Iter>& __i)
: _M_current(__i.base()) { }
+#if __cplusplus <= 201703L
_GLIBCXX17_CONSTEXPR iterator_type
base() const
{ return _M_current; }
+#else
+ constexpr iterator_type
+ base() const &
+#if __cpp_lib_concepts
+ requires copy_constructible<iterator_type>
+#endif
+ { return _M_current; }
+
+ constexpr iterator_type
+ base() &&
+ { return std::move(_M_current); }
+#endif
_GLIBCXX17_CONSTEXPR reference
operator*() const
--
2.25.0.114.g5b0ca878e0
