[PATCH] libstdc++: P1983R0 Wording for GB301, US296, US292, US291, and US283

[PATCH] libstdc++: P1983R0 Wording for GB301, US296, US292, US291, and US283

[Patrick Palka]

Among other changes, P1983R0 resolves LWG 3278 in a different way, so this patch
also reverts the already-applied change of LWG 3278.

The wording for US283 has already been applied it seems.

libstdc++-v3/ChangeLog:

	P1983R0 Wording for GB301, US296, US292, US291, and US283
	* include/std/ranges (filter_view::pred): New member function.
	(join_view::_Iterator::_Iterator): Remove now-redundant comment since
	P1983R0 fixes the highlighted issue in the same way.
	(join_view::_M_inner): Remove mutable specifier, effectively reverting
	the proposed wording changes of P3278.
	(join_view::begin): Refine the condition for when to return a const
	iterator.
	(split_view::_OuterIter::_OuterIter): Adjust constraints.
	* testsuite/std/ranges/adaptors/filter.cc: Test that filter_view::pred
	exists and works.
---
 libstdc++-v3/include/std/ranges                | 18 ++++++++++--------
 .../testsuite/std/ranges/adaptors/filter.cc    |  2 ++
 2 files changed, 12 insertions(+), 8 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index a04387a75c4..2f090dbd9fb 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1556,6 +1556,10 @@ namespace views
       base() &&
       { return std::move(_M_base); }
 
+      constexpr const _Pred&
+      pred() const
+      { return *_M_pred; }
+
       constexpr _Iterator
       begin()
       {
@@ -2421,8 +2425,6 @@ namespace views
 
 	  _Iterator() = default;
 
-	  // XXX: had to change the type of __outer from iterator_t<_Vp> to
-	  // iterator_t<_Base> here, a possible defect in the spec?
 	  constexpr
 	  _Iterator(_Parent& __parent, iterator_t<_Base> __outer)
 	    : _M_outer(std::move(__outer)),
@@ -2560,9 +2562,7 @@ namespace views
 
       _Vp _M_base = _Vp();
 
-      // XXX: _M_inner is "present only when !is_reference_v<_InnerRange>"
-      // Applied P3278 and made this field mutable.
-      [[no_unique_address]] mutable
+      [[no_unique_address]]
 	conditional_t<!is_reference_v<_InnerRange>,
 		      all_view<_InnerRange>, __detail::_Empty> _M_inner;
 
@@ -2595,8 +2595,10 @@ namespace views
       constexpr auto
       begin()
       {
-	return _Iterator<__detail::__simple_view<_Vp>>{*this,
-						       ranges::begin(_M_base)};
+	constexpr bool __use_const
+	  = (__detail::__simple_view<_Vp>
+	     && is_reference_v<range_reference_t<_Vp>>);
+	return _Iterator<__use_const>{*this, ranges::begin(_M_base)};
       }
 
       constexpr auto
@@ -2762,7 +2764,7 @@ namespace views
 	  constexpr
 	  _OuterIter(_OuterIter<!_Const> __i)
 	    requires _Const
-	      && convertible_to<iterator_t<_Vp>, iterator_t<const _Vp>>
+	      && convertible_to<iterator_t<_Vp>, iterator_t<_Base>>
 	    : _M_parent(__i._M_parent), _M_current(std::move(__i._M_current))
 	  { }
 
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
index 834d10f7f91..84858798dda 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
@@ -48,6 +48,8 @@ test01()
   static_assert(ranges::range<ranges::all_view<R>>);
   VERIFY( ranges::equal(v, (int[]){1,3,5}) );
   VERIFY( ranges::equal(v | views::reverse, (int[]){5,3,1}) );
+  VERIFY( v.pred()(3) == true );
+  VERIFY( v.pred()(4) == false );
 }
 
 void
-- 
2.25.1.291.ge68e29171c

Re: [PATCH] libstdc++: P1983R0 Wording for GB301, US296, US292, US291, and US283

[Patrick Palka]

On Tue, 18 Feb 2020, Patrick Palka wrote:

> Among other changes, P1983R0 resolves LWG 3278 in a different way, so this patch
> also reverts the already-applied change of LWG 3278.
> 
> The wording for US283 has already been applied it seems.
> 
> libstdc++-v3/ChangeLog:
> 
> 	P1983R0 Wording for GB301, US296, US292, US291, and US283
> 	* include/std/ranges (filter_view::pred): New member function.
> 	(join_view::_Iterator::_Iterator): Remove now-redundant comment since
> 	P1983R0 fixes the highlighted issue in the same way.
> 	(join_view::_M_inner): Remove mutable specifier, effectively reverting
> 	the proposed wording changes of P3278.
> 	(join_view::begin): Refine the condition for when to return a const
> 	iterator.
> 	(split_view::_OuterIter::_OuterIter): Adjust constraints.
> 	* testsuite/std/ranges/adaptors/filter.cc: Test that filter_view::pred
> 	exists and works.

Oops, this patch is incomplete, it breaks the join_view adaptor test due
to a missing friend, sorry about that.  Here's the complete and tested
patch:

-- >8 --

Subject: [PATCH] libstdc++: P1983R0 Wording for GB301, US296, US292, US291,
 and US283

Among other changes, P1983R0 resolves LWG 3278 in a different way, so this patch
also reverts the already-applied change of LWG 3278.

The wording for US291 (the join_view::begin hunk) also required adding the
friend _Iterator<!_Const> to join::view::_Iterator.  This friend is required for
one of this iterator's converting constructors to be able to access the private
members of an _Iterator of the opposite constness.

The wording for US283 has already been applied it seems.

libstdc++-v3/ChangeLog:

	P1983R0 Wording for GB301, US296, US292, US291, and US283
	* include/std/ranges (filter_view::pred): New member function.
	(join_view::_Iterator::_Iterator): Remove now-redundant comment since
	P1983R0 fixes the highlighted issue in the same way.
	(join_view::_Iterator<_Const>): Add friend
	join_view::_Iterator<!_Const>.
	(join_view::_M_inner): Remove mutable specifier, effectively reverting
	the proposed wording changes of P3278.
	(join_view::begin): Refine the condition for when to return a const
	iterator.
	(split_view::_OuterIter::_OuterIter): Adjust constraints.
	* testsuite/std/ranges/adaptors/filter.cc: Test that filter_view::pred
	exists and works.
---
 libstdc++-v3/include/std/ranges                | 18 +++++++++++-------
 .../testsuite/std/ranges/adaptors/filter.cc    |  2 ++
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index a04387a75c4..fb6e67dd0b3 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -1556,6 +1556,10 @@ namespace views
       base() &&
       { return std::move(_M_base); }
 
+      constexpr const _Pred&
+      pred() const
+      { return *_M_pred; }
+
       constexpr _Iterator
       begin()
       {
@@ -2421,8 +2425,6 @@ namespace views
 
 	  _Iterator() = default;
 
-	  // XXX: had to change the type of __outer from iterator_t<_Vp> to
-	  // iterator_t<_Base> here, a possible defect in the spec?
 	  constexpr
 	  _Iterator(_Parent& __parent, iterator_t<_Base> __outer)
 	    : _M_outer(std::move(__outer)),
@@ -2523,6 +2525,7 @@ namespace views
 	    noexcept(noexcept(ranges::iter_swap(__x._M_inner, __y._M_inner)))
 	  { return ranges::iter_swap(__x._M_inner, __y._M_inner); }
 
+	  friend _Iterator<!_Const>;
 	  friend _Sentinel<_Const>;
 	};
 
@@ -2561,8 +2564,7 @@ namespace views
       _Vp _M_base = _Vp();
 
       // XXX: _M_inner is "present only when !is_reference_v<_InnerRange>"
-      // Applied P3278 and made this field mutable.
-      [[no_unique_address]] mutable
+      [[no_unique_address]]
 	conditional_t<!is_reference_v<_InnerRange>,
 		      all_view<_InnerRange>, __detail::_Empty> _M_inner;
 
@@ -2595,8 +2597,10 @@ namespace views
       constexpr auto
       begin()
       {
-	return _Iterator<__detail::__simple_view<_Vp>>{*this,
-						       ranges::begin(_M_base)};
+	constexpr bool __use_const
+	  = (__detail::__simple_view<_Vp>
+	     && is_reference_v<range_reference_t<_Vp>>);
+	return _Iterator<__use_const>{*this, ranges::begin(_M_base)};
       }
 
       constexpr auto
@@ -2762,7 +2766,7 @@ namespace views
 	  constexpr
 	  _OuterIter(_OuterIter<!_Const> __i)
 	    requires _Const
-	      && convertible_to<iterator_t<_Vp>, iterator_t<const _Vp>>
+	      && convertible_to<iterator_t<_Vp>, iterator_t<_Base>>
 	    : _M_parent(__i._M_parent), _M_current(std::move(__i._M_current))
 	  { }
 
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
index 834d10f7f91..84858798dda 100644
--- a/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/filter.cc
@@ -48,6 +48,8 @@ test01()
   static_assert(ranges::range<ranges::all_view<R>>);
   VERIFY( ranges::equal(v, (int[]){1,3,5}) );
   VERIFY( ranges::equal(v | views::reverse, (int[]){5,3,1}) );
+  VERIFY( v.pred()(3) == true );
+  VERIFY( v.pred()(4) == false );
 }
 
 void
-- 
2.25.1.291.ge68e29171c

Re: [PATCH] libstdc++: P1983R0 Wording for GB301, US296, US292, US291, and US283

[Jonathan Wakely]

On 18/02/20 14:31 -0500, Patrick Palka wrote:
>On Tue, 18 Feb 2020, Patrick Palka wrote:
>
>> Among other changes, P1983R0 resolves LWG 3278 in a different way, so this patch
>> also reverts the already-applied change of LWG 3278.
>>
>> The wording for US283 has already been applied it seems.
>>
>> libstdc++-v3/ChangeLog:
>>
>> 	P1983R0 Wording for GB301, US296, US292, US291, and US283
>> 	* include/std/ranges (filter_view::pred): New member function.
>> 	(join_view::_Iterator::_Iterator): Remove now-redundant comment since
>> 	P1983R0 fixes the highlighted issue in the same way.
>> 	(join_view::_M_inner): Remove mutable specifier, effectively reverting
>> 	the proposed wording changes of P3278.
>> 	(join_view::begin): Refine the condition for when to return a const
>> 	iterator.
>> 	(split_view::_OuterIter::_OuterIter): Adjust constraints.
>> 	* testsuite/std/ranges/adaptors/filter.cc: Test that filter_view::pred
>> 	exists and works.
>
>Oops, this patch is incomplete, it breaks the join_view adaptor test due
>to a missing friend, sorry about that.  Here's the complete and tested
>patch:

OK for master, thanks.