This implements P3913R1: Optimize for std::optional in range adaptors.
Specifically, for an opt of type optional<T> that is a view:
* views::reverse(opt), views::take(opt, n), and views::drop(opt, n) returns
optional<T>.
* views::as_const(opt), optional<T&> is converted into optional<const T&>.
optional<T const> is not used in the non-reference case because, such
type is not move assignable, and thus not a view.
libstdc++-v3/ChangeLog:
* include/std/optional (__is_optional_ref_v): Define.
* include/std/ranges (_Take::operator(), _Drop::operator())
(_Reverse::operator()): Handle optional<T> that are view.
(_AsConst::operator()): Handle optional<T&>.
* testsuite/20_util/optional/range.cc: New tests.
---
The changes got approved for C++26 so submitting this as proper patch.
v3 expands existing test cases, to cover references to NonMovable and
NonAssingable types. Use TEST_ADAPTOR macro to generate test cases
for adaptors (except ranges::as_const).
Tested on x86_64-linux locally. *optional* test also tested with all
supported standard modes. OK for trunk?
libstdc++-v3/include/std/optional | 8 +-
libstdc++-v3/include/std/ranges | 16 ++
.../testsuite/20_util/optional/range.cc | 161 +++++++++++++++++-
3 files changed, 179 insertions(+), 6 deletions(-)
diff --git a/libstdc++-v3/include/std/optional
b/libstdc++-v3/include/std/optional
index 75a9531ccd5..41c04b10720 100644
--- a/libstdc++-v3/include/std/optional
+++ b/libstdc++-v3/include/std/optional
@@ -1486,6 +1486,12 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
template<typename _Tp>
class optional<_Tp&>;
+ template<typename _Tp>
+ constexpr bool __is_optional_ref_v = false;
+
+ template<typename _Tp>
+ constexpr bool __is_optional_ref_v<optional<_Tp&>> = true;
+
template<typename _Tp>
struct __optional_ref_base
{};
@@ -2187,7 +2193,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
constexpr bool
ranges::enable_borrowed_range<optional<_Tp&>> = true;
#endif
-
+
template<typename _Tp>
inline constexpr range_format
format_kind<optional<_Tp>> = range_format::disabled;
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 158692d92a7..ae57b9a0809 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -2403,6 +2403,10 @@ namespace views::__adaptor
using _Tp = remove_cvref_t<_Range>;
if constexpr (__detail::__is_empty_view<_Tp>)
return _Tp();
+#ifdef __cpp_lib_optional_range_support // >= C++26
+ else if constexpr (__is_optional_v<_Tp> && view<_Tp>)
+ return __n ? std::forward<_Range>(__r) : _Tp();
+#endif
else if constexpr (random_access_range<_Tp>
&& sized_range<_Tp>
&& (std::__detail::__is_span<_Tp>
@@ -2679,6 +2683,10 @@ namespace views::__adaptor
using _Tp = remove_cvref_t<_Range>;
if constexpr (__detail::__is_empty_view<_Tp>)
return _Tp();
+#ifdef __cpp_lib_optional_range_support // >= C++26
+ else if constexpr (__is_optional_v<_Tp> && view<_Tp>)
+ return __n ? _Tp() : std::forward<_Range>(__r);
+#endif
else if constexpr (random_access_range<_Tp>
&& sized_range<_Tp>
&& (std::__detail::__is_span<_Tp>
@@ -4156,6 +4164,10 @@ namespace views::__adaptor
using _Tp = remove_cvref_t<_Range>;
if constexpr (__detail::__is_reverse_view<_Tp>)
return std::forward<_Range>(__r).base();
+#ifdef __cpp_lib_optional_range_support // >= C++26
+ else if constexpr (__is_optional_v<_Tp> && view<_Tp>)
+ return std::forward<_Range>(__r);
+#endif
else if constexpr (__detail::__is_reversible_subrange<_Tp>)
{
using _Iter = decltype(ranges::begin(__r).base());
@@ -9312,6 +9324,10 @@ namespace views::__adaptor
return views::all(std::forward<_Range>(__r));
else if constexpr (__detail::__is_empty_view<_Tp>)
return views::empty<const element_type>;
+#if __cpp_lib_optional >= 202506L && __cpp_lib_optional_range_support // >=
C++26
+ else if constexpr (__is_optional_ref_v<_Tp>)
+ return optional<const typename _Tp::value_type&>(__r);
+#endif
else if constexpr (std::__detail::__is_span<_Tp>)
return span<const element_type,
_Tp::extent>(std::forward<_Range>(__r));
else if constexpr (__detail::__is_constable_ref_view<_Tp>)
diff --git a/libstdc++-v3/testsuite/20_util/optional/range.cc
b/libstdc++-v3/testsuite/20_util/optional/range.cc
index 981969cb614..4238c9cf28e 100644
--- a/libstdc++-v3/testsuite/20_util/optional/range.cc
+++ b/libstdc++-v3/testsuite/20_util/optional/range.cc
@@ -10,6 +10,26 @@
#include <testsuite_hooks.h>
+struct NonMovable
+{
+ constexpr NonMovable() {}
+ constexpr NonMovable(int) {}
+
+ NonMovable(NonMovable&&) = delete;
+ NonMovable& operator=(NonMovable&&) = delete;
+
+ friend bool operator==(NonMovable const&, NonMovable const&) = default;
+};
+
+struct NonAssignable
+{
+ NonAssignable() = default;
+ NonAssignable(NonAssignable&&) = default;
+ NonAssignable& operator=(NonAssignable&&) = delete;
+
+ friend bool operator==(NonAssignable const&, NonAssignable const&) = default;
+};
+
template<typename T>
constexpr
void
@@ -24,10 +44,11 @@ test_range_concepts()
constexpr bool is_ref_opt = std::is_reference_v<T>;
static_assert(std::ranges::borrowed_range<O> == is_ref_opt);
- // an optional<const T> is not assignable, and therefore does not satisfy
ranges::view
- constexpr bool is_const_opt = std::is_const_v<T>;
- static_assert(std::ranges::view<O> == !is_const_opt);
- static_assert(std::ranges::viewable_range<O> == !is_const_opt);
+ // for any T (including const U) such that optional<T> is not assignable,
+ // it does not satisfy ranges::view
+ constexpr bool is_opt_view = std::is_reference_v<T> || std::movable<T>;
+ static_assert(std::ranges::view<O> == is_opt_view);
+ static_assert(std::ranges::viewable_range<O> == is_opt_view);
}
@@ -108,7 +129,7 @@ test_non_empty(const T& value)
++count;
VERIFY(count == 1);
- if constexpr (!std::is_const_v<V> && !std::is_array_v<V>) {
+ if constexpr (std::is_move_assignable_v<V>) {
for (auto& x : non_empty)
x = V{};
VERIFY(non_empty);
@@ -168,6 +189,99 @@ constexpr void test_not_range()
static_assert(!requires(std::optional<T> o) { o.end(); });
};
+template<typename T>
+constexpr bool is_optional = false;
+
+template<typename T>
+constexpr bool is_optional<std::optional<T>> = true;
+
+template<bool usesOptional, typename T, typename U = std::remove_cv_t<T>>
+constexpr void test_as_const(std::type_identity_t<U> u)
+{
+ std::optional<T> o(std::in_place, std::forward<U>(u));
+ auto cv = std::views::as_const(o);
+ static_assert(is_optional<decltype(cv)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*cv.begin()), const
std::remove_reference_t<T>&>);
+ VERIFY(!std::ranges::empty(cv));
+
+ std::optional<T> e;
+ auto cve = std::views::as_const(e);
+ static_assert(is_optional<decltype(cve)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*cve.begin()), const
std::remove_reference_t<T>&>);
+ VERIFY(std::ranges::empty(cve));
+}
+
+template<bool usesOptional, typename T, typename U = std::remove_cv_t<T>>
+constexpr void
+test_reverse(std::type_identity_t<U> u)
+{
+ std::optional<T> o(std::in_place, std::forward<U>(u));
+ auto rv = std::views::reverse(o);
+ static_assert(is_optional<decltype(rv)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*rv.begin()), T&>);
+ VERIFY(!std::ranges::empty(rv));
+
+ std::optional<T> e;
+ auto rve = std::views::reverse(e);
+ static_assert(is_optional<decltype(rve)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*rve.begin()), T&>);
+ VERIFY(std::ranges::empty(rve));
+}
+
+template<bool usesOptional, typename T, typename U = std::remove_cv_t<T>>
+constexpr void
+test_take(std::type_identity_t<U> u)
+{
+ std::optional<T> o(std::in_place, std::forward<U>(u));
+ auto tvp = std::views::take(o, 3);
+ static_assert(is_optional<decltype(tvp)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*tvp.begin()), T&>);
+ VERIFY(!std::ranges::empty(tvp));
+
+ auto tvz = std::views::take(o, 0);
+ static_assert(is_optional<decltype(tvz)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*tvz.begin()), T&>);
+ VERIFY(std::ranges::empty(tvz));
+
+ std::optional<T> e;
+ auto tvep = std::views::take(e, 5);
+ static_assert(is_optional<decltype(tvep)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*tvep.begin()), T&>);
+ VERIFY(std::ranges::empty(tvep));
+
+ auto tvez = std::views::take(e, 0);
+ static_assert(is_optional<decltype(tvez)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*tvez.begin()), T&>);
+ VERIFY(std::ranges::empty(tvez));
+}
+
+template<bool usesOptional, typename T, typename U = std::remove_cv_t<T>>
+constexpr void
+test_drop(std::type_identity_t<U> u)
+{
+ std::optional<T> o(std::in_place, std::forward<U>(u));
+ auto dvp = std::views::drop(o, 3);
+ static_assert(is_optional<decltype(dvp)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*dvp.begin()), T&>);
+ VERIFY(std::ranges::empty(dvp));
+
+ auto dvz = std::views::drop(o, 0);
+ static_assert(is_optional<decltype(dvz)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*dvz.begin()), T&>);
+ VERIFY(!std::ranges::empty(dvz));
+
+ std::optional<T> e;
+ auto dvep = std::views::drop(e, 5);
+ static_assert(is_optional<decltype(dvep)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*dvep.begin()), T&>);
+ VERIFY(std::ranges::empty(dvep));
+
+ auto dvez = std::views::drop(e, 0);
+ static_assert(is_optional<decltype(dvez)> == usesOptional);
+ static_assert(std::is_same_v<decltype(*dvez.begin()), T&>);
+ VERIFY(std::ranges::empty(dvez));
+}
+
constexpr
bool
all_tests()
@@ -175,6 +289,8 @@ all_tests()
test(42);
int i = 42;
int arr[10]{};
+ NonMovable nm;
+ NonAssignable na;
test(&i);
test(std::string_view("test"));
test(std::vector<int>{1, 2, 3, 4});
@@ -185,6 +301,10 @@ all_tests()
test<const int&>(i);
test<int(&)[10]>(arr);
test<const int(&)[10]>(arr);
+ test<NonMovable&>(nm);
+ test<const NonMovable&>(nm);
+ test<NonAssignable&>(na);
+ test<const NonAssignable&>(na);
test_not_range<void(&)()>();
test_not_range<void(&)(int)>();
test_not_range<int(&)[]>();
@@ -192,6 +312,37 @@ all_tests()
range_chain_example();
+ test_as_const<false, int>(i);
+ test_as_const<false, const int>(i);
+ test_as_const<true, int&>(i);
+ test_as_const<true, const int&>(i);
+ test_as_const<false, NonMovable, int>(10);
+ test_as_const<false, const NonMovable, int>(10);
+ test_as_const<true, NonMovable&>(nm);
+ test_as_const<true, const NonMovable&>(nm);
+ test_as_const<false, NonAssignable>({});
+ test_as_const<false, const NonAssignable>({});
+ test_as_const<true, NonAssignable&>(na);
+ test_as_const<true, const NonAssignable&>(na);
+
+#define TEST_ADAPTOR(name) \
+ test_##name<true, int>(i); \
+ test_##name<false, const int>(i); \
+ test_##name<true, int&>(i); \
+ test_##name<true, const int&>(i); \
+ test_##name<false, NonMovable, int>(10); \
+ test_##name<false, const NonMovable, int>(10); \
+ test_##name<true, NonMovable&>(nm); \
+ test_##name<true, const NonMovable&>(nm); \
+ test_##name<false, NonAssignable>({}); \
+ test_##name<false, const NonAssignable>({}); \
+ test_##name<true, NonAssignable&>(na); \
+ test_##name<true, const NonAssignable&>(na)
+
+ TEST_ADAPTOR(reverse);
+ TEST_ADAPTOR(take);
+ TEST_ADAPTOR(drop);
+#undef TEST_ADAPTOR
return true;
}
--
2.51.0
