[gcc r10-10808] libstdc++: Implement P2325 changes to default-constructibility of views
Patrick Palka
ppalka@gcc.gnu.org
Tue May 31 18:39:39 GMT 2022
https://gcc.gnu.org/g:22b86cdc4d7fddb4991a08515e47e66fe5c41def
commit r10-10808-g22b86cdc4d7fddb4991a08515e47e66fe5c41def
Author: Patrick Palka <ppalka@redhat.com>
Date: Tue May 31 14:38:11 2022 -0400
libstdc++: Implement P2325 changes to default-constructibility of views
NB: This backport of r12-1606 to the 10 branch deliberately omits parts
of P2325R3 so as to maximize backward compatibility with pre-P2325R3 code.
In particular, we don't remove the default ctors for back_insert_iterator,
front_insert_iterator, ostream_iterator, ref_view and basic_istream_view.
And in the 10 branch we we don't have __non_propagating_cache or the
partial specialization of __box, so the changes to them are omitted too.
Finally, we don't update __cpp_lib_ranges to 202106L because many
significant 202106 Ranges changes still aren't implemented in the 10
branch, e.g. P2281R1 and P2210R2.
===
This implements the wording changes of P2325R3 "Views should not be
required to be default constructible". Changes are relatively
straightforward, besides perhaps those to __box (which now stands
for copyable-box instead of semiregular-box) and __non_propagating_cache.
For __box, this patch implements the recommended practice to also avoid
std::optional when the boxed type is nothrow_move/copy_constructible.
For __non_propagating_cache, now that it's used by split_view::_M_current,
we need to add assignment from a value of the underlying type to the
subset of the std::optional API implemented for the cache (needed by
split_view::begin()). Hence the new __non_propagating_cache::operator=
overload.
In passing, this fixes the undesirable list-init in the constructors of
the partial specialization of __box as reported in PR100475 comment #7.
PR libstdc++/103904
libstdc++-v3/ChangeLog:
* include/bits/iterator_concepts.h (weakly_incrementable): Remove
default_initializable requirement.
* include/bits/stl_iterator.h (common_iterator): Constrain the
default ctor.
(counted_iterator): Likewise.
* include/std/ranges (ranges::view): Remove default_initializable
requirement.
(subrange): Constrain the default ctor.
(__detail::__box::operator=): Handle self-assignment.
(single_view): Constraint the default ctor.
(iota_view): Relax semiregular constraint to copyable.
Constrain the default ctor.
(iota_view::_Iterator): Constraint the default ctor.
(filter_view): Likewise.
(filter_view::_Iterator): Likewise.
(transform_view): Likewise.
(transform_view::_Iterator): Likewise.
(take_view): Likewise.
(take_view::_Iterator): Likewise.
(take_while_view): Likewise.
(take_while_view::_Iterator): Likewise.
(drop_while_view): Likewise.
(drop_while_view::_Iterator): Likewise.
(join_view): Likewise.
(split_view): Constrain the default ctor.
(common_view): Likewise.
(reverse_view): Likewise.
(elements_view): Likewise.
(elements_view::_Iterator): Likewise.
* include/std/span (enable_view<span<_ElementType, _Extent>>):
Define this partial specialization to true unconditionally.
* testsuite/std/ranges/p2325.cc: New test.
* testsuite/std/ranges/single_view.cc (test06): New test.
* testsuite/std/ranges/view.cc: Adjust now that view doesn't
require default_initializable.
(cherry picked from commit 4b4f5666b4c2f3aab2a9f3d53d394e390b9b682d)
Diff:
---
libstdc++-v3/include/bits/iterator_concepts.h | 3 +-
libstdc++-v3/include/bits/stl_iterator.h | 3 +-
libstdc++-v3/include/std/ranges | 78 ++++++----
libstdc++-v3/include/std/span | 3 +-
libstdc++-v3/testsuite/std/ranges/p2325.cc | 181 +++++++++++++++++++++++
libstdc++-v3/testsuite/std/ranges/single_view.cc | 15 ++
libstdc++-v3/testsuite/std/ranges/view.cc | 2 +-
7 files changed, 249 insertions(+), 36 deletions(-)
diff --git a/libstdc++-v3/include/bits/iterator_concepts.h b/libstdc++-v3/include/bits/iterator_concepts.h
index 4f118df6b02..a533ae2d279 100644
--- a/libstdc++-v3/include/bits/iterator_concepts.h
+++ b/libstdc++-v3/include/bits/iterator_concepts.h
@@ -573,8 +573,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
/// Requirements on types that can be incremented with ++.
template<typename _Iter>
- concept weakly_incrementable = default_initializable<_Iter>
- && movable<_Iter>
+ concept weakly_incrementable = movable<_Iter>
&& requires(_Iter __i)
{
typename iter_difference_t<_Iter>;
diff --git a/libstdc++-v3/include/bits/stl_iterator.h b/libstdc++-v3/include/bits/stl_iterator.h
index 91cfeccecf3..a46872fc3c2 100644
--- a/libstdc++-v3/include/bits/stl_iterator.h
+++ b/libstdc++-v3/include/bits/stl_iterator.h
@@ -1729,6 +1729,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr
common_iterator()
noexcept(is_nothrow_default_constructible_v<_It>)
+ requires default_initializable<_It>
: _M_it(), _M_index(0)
{ }
@@ -2106,7 +2107,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// iterator_concept defined in __counted_iter_concept
// iterator_category defined in __counted_iter_cat
- constexpr counted_iterator() = default;
+ constexpr counted_iterator() requires default_initializable<_It> = default;
constexpr
counted_iterator(_It __i, iter_difference_t<_It> __n)
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index cec775db3b1..4c08de39c1d 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -70,8 +70,7 @@ namespace ranges
template<typename _Tp>
concept view
- = range<_Tp> && movable<_Tp> && default_initializable<_Tp>
- && enable_view<_Tp>;
+ = range<_Tp> && movable<_Tp> && enable_view<_Tp>;
/// A range which can be safely converted to a view.
template<typename _Tp>
@@ -251,7 +250,7 @@ namespace ranges
[[no_unique_address]] _Size<iter_difference_t<_It>> _M_size = {};
public:
- subrange() = default;
+ subrange() requires default_initializable<_It> = default;
constexpr
subrange(__detail::__convertible_to_non_slicing<_It> auto __i, _Sent __s)
@@ -486,10 +485,13 @@ namespace ranges
noexcept(is_nothrow_copy_constructible_v<_Tp>)
requires (!copyable<_Tp>)
{
- if ((bool)__that)
- this->emplace(*__that);
- else
- this->reset();
+ if (this != std::__addressof(__that))
+ {
+ if ((bool)__that)
+ this->emplace(*__that);
+ else
+ this->reset();
+ }
return *this;
}
@@ -498,10 +500,13 @@ namespace ranges
noexcept(is_nothrow_move_constructible_v<_Tp>)
requires (!movable<_Tp>)
{
- if ((bool)__that)
- this->emplace(std::move(*__that));
- else
- this->reset();
+ if (this != std::__addressof(__that))
+ {
+ if ((bool)__that)
+ this->emplace(std::move(*__that));
+ else
+ this->reset();
+ }
return *this;
}
};
@@ -513,7 +518,7 @@ namespace ranges
class single_view : public view_interface<single_view<_Tp>>
{
public:
- single_view() = default;
+ single_view() requires default_initializable<_Tp> = default;
constexpr explicit
single_view(const _Tp& __t)
@@ -622,7 +627,7 @@ namespace ranges
template<weakly_incrementable _Winc,
semiregular _Bound = unreachable_sentinel_t>
requires std::__detail::__weakly_eq_cmp_with<_Winc, _Bound>
- && semiregular<_Winc>
+ && copyable<_Winc>
class iota_view : public view_interface<iota_view<_Winc, _Bound>>
{
private:
@@ -651,7 +656,7 @@ namespace ranges
using value_type = _Winc;
using difference_type = __detail::__iota_diff_t<_Winc>;
- _Iterator() = default;
+ _Iterator() requires default_initializable<_Winc> = default;
constexpr explicit
_Iterator(_Winc __value)
@@ -848,7 +853,7 @@ namespace ranges
_Bound _M_bound = _Bound();
public:
- iota_view() = default;
+ iota_view() requires default_initializable<_Winc> = default;
constexpr explicit
iota_view(_Winc __value)
@@ -1475,7 +1480,7 @@ namespace views
using value_type = range_value_t<_Vp>;
using difference_type = range_difference_t<_Vp>;
- _Iterator() = default;
+ _Iterator() requires default_initializable<_Vp_iter> = default;
constexpr
_Iterator(filter_view* __parent, _Vp_iter __current)
@@ -1587,7 +1592,9 @@ namespace views
[[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
public:
- filter_view() = default;
+ filter_view() requires (default_initializable<_Vp>
+ && default_initializable<_Pred>)
+ = default;
constexpr
filter_view(_Vp __base, _Pred __pred)
@@ -1718,7 +1725,7 @@ namespace views
= remove_cvref_t<invoke_result_t<_Fp&, range_reference_t<_Base>>>;
using difference_type = range_difference_t<_Base>;
- _Iterator() = default;
+ _Iterator() requires default_initializable<_Base_iter> = default;
constexpr
_Iterator(_Parent* __parent, _Base_iter __current)
@@ -1933,7 +1940,9 @@ namespace views
__detail::__box<_Fp> _M_fun;
public:
- transform_view() = default;
+ transform_view() requires (default_initializable<_Vp>
+ && default_initializable<_Fp>)
+ = default;
constexpr
transform_view(_Vp __base, _Fp __fun)
@@ -2050,7 +2059,7 @@ namespace views
range_difference_t<_Vp> _M_count = 0;
public:
- take_view() = default;
+ take_view() requires default_initializable<_Vp> = default;
constexpr
take_view(_Vp base, range_difference_t<_Vp> __count)
@@ -2211,7 +2220,9 @@ namespace views
__detail::__box<_Pred> _M_pred;
public:
- take_while_view() = default;
+ take_while_view() requires (default_initializable<_Vp>
+ && default_initializable<_Pred>)
+ = default;
constexpr
take_while_view(_Vp base, _Pred __pred)
@@ -2282,7 +2293,7 @@ namespace views
_M_cached_begin;
public:
- drop_view() = default;
+ drop_view() requires default_initializable<_Vp> = default;
constexpr
drop_view(_Vp __base, range_difference_t<_Vp> __count)
@@ -2378,7 +2389,9 @@ namespace views
[[no_unique_address]] __detail::_CachedPosition<_Vp> _M_cached_begin;
public:
- drop_while_view() = default;
+ drop_while_view() requires (default_initializable<_Vp>
+ && default_initializable<_Pred>)
+ = default;
constexpr
drop_while_view(_Vp __base, _Pred __pred)
@@ -2553,7 +2566,9 @@ namespace views
= common_type_t<range_difference_t<_Base>,
range_difference_t<range_reference_t<_Base>>>;
- _Iterator() = default;
+ _Iterator() requires (default_initializable<_Outer_iter>
+ && default_initializable<_Inner_iter>)
+ = default;
constexpr
_Iterator(_Parent* __parent, _Outer_iter __outer)
@@ -2709,7 +2724,7 @@ namespace views
views::all_t<_InnerRange>> _M_inner;
public:
- join_view() = default;
+ join_view() requires default_initializable<_Vp> = default;
constexpr explicit
join_view(_Vp __base)
@@ -3123,7 +3138,10 @@ namespace views
public:
- split_view() = default;
+ split_view() requires (default_initializable<_Vp>
+ && default_initializable<_Pattern>
+ && default_initializable<iterator_t<_Vp>>)
+ = default;
constexpr
split_view(_Vp __base, _Pattern __pattern)
@@ -3229,7 +3247,7 @@ namespace views
_Vp _M_base = _Vp();
public:
- common_view() = default;
+ common_view() requires default_initializable<_Vp> = default;
constexpr explicit
common_view(_Vp __r)
@@ -3339,7 +3357,7 @@ namespace views
_M_cached_begin;
public:
- reverse_view() = default;
+ reverse_view() requires default_initializable<_Vp> = default;
constexpr explicit
reverse_view(_Vp __r)
@@ -3466,7 +3484,7 @@ namespace views
class elements_view : public view_interface<elements_view<_Vp, _Nm>>
{
public:
- elements_view() = default;
+ elements_view() requires default_initializable<_Vp> = default;
constexpr explicit
elements_view(_Vp base)
@@ -3587,7 +3605,7 @@ namespace views
= remove_cvref_t<tuple_element_t<_Nm, range_value_t<_Base>>>;
using difference_type = range_difference_t<_Base>;
- _Iterator() = default;
+ _Iterator() requires default_initializable<iterator_t<_Base>> = default;
constexpr explicit
_Iterator(iterator_t<_Base> current)
diff --git a/libstdc++-v3/include/std/span b/libstdc++-v3/include/std/span
index 4b389a46af7..35df1a64c0e 100644
--- a/libstdc++-v3/include/std/span
+++ b/libstdc++-v3/include/std/span
@@ -453,8 +453,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
// Opt-in to view concept
template<typename _ElementType, size_t _Extent>
inline constexpr bool
- enable_view<span<_ElementType, _Extent>>
- = _Extent == 0 || _Extent == dynamic_extent;
+ enable_view<span<_ElementType, _Extent>> = true;
}
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
diff --git a/libstdc++-v3/testsuite/std/ranges/p2325.cc b/libstdc++-v3/testsuite/std/ranges/p2325.cc
new file mode 100644
index 00000000000..aff3bd6ca28
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/p2325.cc
@@ -0,0 +1,181 @@
+// { dg-options "-std=gnu++20" }
+// { dg-do compile { target c++20 } }
+// P2325R3 "Views should not be required to be default constructible"
+
+// Parts of P2325R3 are deliberately omitted in libstdc++ 10, in particular the
+// removal of default ctors for back_/front_insert_iterator, ostream_iterator,
+// ref_view and basic_istream_view/::iterator, so as to maximize backward
+// compatibility with pre-P2325R3 code. So most static_asserts in this test fail,
+// see the xfails at the end of this file.
+
+#include <ranges>
+#include <iterator>
+#include <span>
+#include <sstream>
+#include <vector>
+#include <testsuite_iterators.h>
+
+using namespace std;
+
+template<default_initializable T> void f();
+template<typename T> requires weakly_incrementable<T> || ranges::view<T> void f();
+
+void
+test01()
+{
+ // Verify neither std::weakly_incrementable nor ranges::view require
+ // default_initializable.
+ f<int>(); // { dg-error "ambiguous" }
+}
+
+void
+test02()
+{
+ // Verify these iterators are not default constructible.
+ static_assert(!default_initializable<insert_iterator<vector<int>>>);
+ static_assert(!default_initializable<front_insert_iterator<vector<int>>>);
+ static_assert(!default_initializable<back_insert_iterator<vector<int>>>);
+ static_assert(!default_initializable<ostream_iterator<int>>);
+
+ using iter = ostream_iterator<int>;
+
+ // Verify common_iterator is conditionally default constructible.
+ static_assert(!default_initializable<common_iterator<iter, unreachable_sentinel_t>>);
+ static_assert(default_initializable<common_iterator<int*, unreachable_sentinel_t>>);
+
+ // Verify counted_iterator is conditionally default constructible.
+ static_assert(!default_initializable<counted_iterator<iter>>);
+ static_assert(default_initializable<counted_iterator<int*>>);
+}
+
+void
+test03()
+{
+ using iter = ostream_iterator<int>;
+
+ // Verify iota_view is conditionally default constructible.
+ static_assert(!default_initializable<ranges::iota_view<iter>>);
+ static_assert(!default_initializable<decltype(declval<ranges::iota_view<iter>>().begin())>);
+ static_assert(default_initializable<ranges::iota_view<int>>);
+ static_assert(default_initializable<decltype(declval<ranges::iota_view<int>>().begin())>);
+
+ // Verify subrange is conditionally default constructible.
+ static_assert(!default_initializable<ranges::subrange<iter, unreachable_sentinel_t>>);
+ static_assert(default_initializable<ranges::subrange<int*, unreachable_sentinel_t>>);
+
+ // Verify single_view is conditionally default constructible.
+ static_assert(!default_initializable<ranges::single_view<iter>>);
+ static_assert(default_initializable<ranges::single_view<int*>>);
+}
+
+void
+test04()
+{
+ // Verify basic_istream_view is not default constructible.
+ using type = ranges::basic_istream_view<int, char, char_traits<char>>;
+ static_assert(!default_initializable<type>);
+ static_assert(!default_initializable<decltype(declval<type>().begin())>);
+}
+
+void
+test05()
+{
+ // Verify ref_view is not default constructible.
+ static_assert(!default_initializable<ranges::ref_view<int[5]>>);
+}
+
+template<auto& adaptor>
+void
+test06()
+{
+ auto f1 = [] (auto) { return true; };
+ auto f2 = [i=0] (auto) { return true; };
+ static_assert(default_initializable<decltype(views::single(0) | adaptor(f1))>);
+ static_assert(!default_initializable<decltype(views::single(0) | adaptor(f2))>);
+
+ struct S { S() = delete; };
+ static_assert(!default_initializable<decltype(views::single(declval<S>()) | adaptor(f1))>);
+ static_assert(!default_initializable<decltype(views::single(declval<S>()) | adaptor(f2))>);
+}
+
+// Verify filter_view, transform_view, take_while_view and drop_while_view are
+// conditionally default constructible.
+template void test06<views::filter>();
+template void test06<views::transform>();
+template void test06<views::take_while>();
+template void test06<views::drop_while>();
+
+void
+test07()
+{
+ // Verify join_view is conditionally default constructible.
+ struct S { S() = delete; };
+ using type1 = ranges::join_view<ranges::single_view<ranges::single_view<S>>>;
+ static_assert(!default_initializable<type1>);
+ using type2 = ranges::join_view<ranges::single_view<ranges::single_view<int>>>;
+ static_assert(default_initializable<type2>);
+}
+
+void
+test08()
+{
+ // Verify split_view is conditionally default constructible.
+ using type1 = ranges::split_view<ranges::ref_view<int[2]>, ranges::single_view<int>>;
+ static_assert(!default_initializable<type1>);
+ using type2 = ranges::split_view<ranges::single_view<int>, ranges::ref_view<int[2]>>;
+ static_assert(!default_initializable<type2>);
+ using type3 = ranges::split_view<ranges::ref_view<int[2]>, ranges::ref_view<int[2]>>;
+ static_assert(!default_initializable<type3>);
+ using type4 = ranges::split_view<ranges::single_view<int>, ranges::single_view<int>>;
+ static_assert(default_initializable<type4>);
+}
+
+void
+test09()
+{
+ // Verify common_view is conditionally default constructible.
+ using type1 = ranges::common_view<ranges::iota_view<ostream_iterator<int>>>;
+ static_assert(!default_initializable<type1>);
+ using type2 = ranges::common_view<ranges::iota_view<int*>>;
+ static_assert(default_initializable<type2>);
+}
+
+void
+test10()
+{
+ // Verify reverse_view is conditionally default constructible.
+ using type1 = ranges::reverse_view<ranges::ref_view<int[2]>>;
+ static_assert(!default_initializable<type1>);
+ using type2 = ranges::reverse_view<ranges::single_view<int>>;
+ static_assert(default_initializable<type2>);
+}
+
+void
+test11()
+{
+ // Verify elements_view is conditionally default constructible.
+ using type1 = ranges::elements_view<ranges::ref_view<pair<int,int>[2]>, 0>;
+ static_assert(!default_initializable<type1>);
+ using type2 = ranges::elements_view<ranges::single_view<pair<int,int>>, 0>;
+ static_assert(default_initializable<type2>);
+}
+
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 35 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 36 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 37 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 38 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 43 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 47 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 57 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 58 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 63 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 67 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 76 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 77 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 84 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 124 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 126 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 128 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 138 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 148 }
+// { dg-bogus "static assertion failed" "" { xfail *-*-* } 158 }
diff --git a/libstdc++-v3/testsuite/std/ranges/single_view.cc b/libstdc++-v3/testsuite/std/ranges/single_view.cc
index 658e0a0a32d..48406447060 100644
--- a/libstdc++-v3/testsuite/std/ranges/single_view.cc
+++ b/libstdc++-v3/testsuite/std/ranges/single_view.cc
@@ -58,9 +58,24 @@ test03()
VERIFY(*std::ranges::begin(s3) == 'a');
}
+void
+test06()
+{
+ // PR libstdc++/100475 comment #7
+ struct S {
+ S() = default;
+ S(std::initializer_list<S>) = delete;
+ S(const S&) {}
+ };
+ S obj;
+ auto x = std::views::single(obj);
+ auto y = std::views::single(std::move(obj));
+}
+
int main()
{
test01();
test02();
test03();
+ test06();
}
diff --git a/libstdc++-v3/testsuite/std/ranges/view.cc b/libstdc++-v3/testsuite/std/ranges/view.cc
index 72e8bcb50d7..095a92e466f 100644
--- a/libstdc++-v3/testsuite/std/ranges/view.cc
+++ b/libstdc++-v3/testsuite/std/ranges/view.cc
@@ -31,7 +31,7 @@
static_assert(std::ranges::view<std::span<int>>);
static_assert(std::ranges::view<std::span<int, 0>>);
-static_assert(!std::ranges::view<std::span<int, 1>>);
+static_assert(std::ranges::view<std::span<int, 1>>); // Changed with P2325R3
static_assert(std::ranges::view<std::string_view>);
static_assert(std::ranges::view<std::experimental::string_view>);
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