[PATCH] libstdc++: Add missing bits of P0896R4 pertaining to [back|front]_insert_iterator

[Jonathan Wakely]

On 24/02/20 08:53 -0500, Patrick Palka wrote:
>On Mon, 24 Feb 2020, Jonathan Wakely wrote:
>
>> On 24/02/20 08:29 -0500, Patrick Palka wrote:
>> > This adds some missing pieces of the Ranges TS that make
>> > back_insert_iterator and
>> > front_insert_iterator conform to the new output_iterator requirements.
>> >
>> > It also fixes a bug in ranges::__copy_or_move and
>> > ranges::__copy_or_move_backward in which we were inspecting the iter_value_t
>> > of
>> > the output iterator, but iterators such as back_insert_iterator and
>> > front_insert_iterator whose value_type is defined to be void do not have an
>> > iter_value_t according to [readable.traits] p4.  The entire __use_memmove
>> > condition can probably be refactored, but the simplest fix for now is to
>> > inspect
>> > the iterator_traits of the output iterator instead.
>> >
>> > libstdc++-v3/ChangeLog:
>> >
>> > 	PR libstdc++/93884
>> > 	* include/bits/ranges_algobase.h (__copy_or_move,
>> > 	__copy_or_move_backward): Don't inspect the iter_value_t of the output
>> > 	iterator, instead inspect its iterator_traits directly.
>> > 	* include/bits/stl_iterator.h (back_insert_iterator::container):
>> > 	Conditionally initialize.
>> > 	(back_insert_iterator::difference_type): Conditionally define.
>> > 	(back_insert_iterator::back_insert_iterator): Conditionally define
>> > this
>> > 	default constructor.
>> > 	(front_insert_iterator::container): Conditionally initialize.
>> > 	(front_insert_iterator::difference_type): Conditionally define.
>> > 	(front_insert_iterator::front_insert_iterator): Conditionally define
>> > 	this default constructor.
>> > ---
>> > libstdc++-v3/include/bits/ranges_algobase.h   |  4 +-
>> > libstdc++-v3/include/bits/stl_iterator.h      | 22 ++++++++++
>> > .../back_insert_iterator/pr93884.C            | 44 +++++++++++++++++++
>> > .../front_insert_iterator/pr93884.C           | 44 +++++++++++++++++++
>> > 4 files changed, 112 insertions(+), 2 deletions(-)
>> > create mode 100644
>> > libstdc++-v3/testsuite/24_iterators/back_insert_iterator/pr93884.C
>> > create mode 100644
>> > libstdc++-v3/testsuite/24_iterators/front_insert_iterator/pr93884.C
>> >
>> > diff --git a/libstdc++-v3/include/bits/ranges_algobase.h
>> > b/libstdc++-v3/include/bits/ranges_algobase.h
>> > index 807822e99c8..739424e1a2d 100644
>> > --- a/libstdc++-v3/include/bits/ranges_algobase.h
>> > +++ b/libstdc++-v3/include/bits/ranges_algobase.h
>> > @@ -249,7 +249,7 @@ namespace ranges
>> >       else if constexpr (sized_sentinel_for<_Sent, _Iter>)
>> > 	{
>> > 	  using _ValueTypeI = iter_value_t<_Iter>;
>> > -	  using _ValueTypeO = iter_value_t<_Out>;
>> > +	  using _ValueTypeO = iterator_traits<_Out>::value_type;
>>
>> I think this will fail to compile with Clang, because it needs
>> 'typename' there.
>>
>> > 	  constexpr bool __use_memmove
>> > 	    = (is_trivially_copyable_v<_ValueTypeI>
>> > 	       && is_same_v<_ValueTypeI, _ValueTypeO>
>> > @@ -386,7 +386,7 @@ namespace ranges
>> >       else if constexpr (sized_sentinel_for<_Sent, _Iter>)
>> > 	{
>> > 	  using _ValueTypeI = iter_value_t<_Iter>;
>> > -	  using _ValueTypeO = iter_value_t<_Out>;
>> > +	  using _ValueTypeO = iterator_traits<_Out>::value_type;
>>
>> Same here.
>
>Ah right... Here's v2 of the patch that adds typename to those two
>aliases and fixes the file extensions on the tests.

OK for master, thanks.