On Thu, 13 Feb 2025, Jonathan Wakely wrote:
> On Tue, 11 Feb 2025 at 05:59, Patrick Palka <ppa...@redhat.com> wrote:
> >
> > Tested on x86_64-pc-linux-gnu, does this look OK for trunk?
> >
> > -- >8 --
> >
> > libstdc++-v3/ChangeLog:
> >
> > * include/bits/version.def (ranges_cache_latest): Define.
> > * include/bits/version.h: Regenerate.
> > * include/std/ranges (cache_latest_view): Define for C++26.
> > (cache_latest_view::_Iterator): Likewise.
> > (cache_latest_view::_Sentinel): Likewise.
> > (views::__detail::__can_cache_latest): Likewise.
> > (views::_CacheLatest, views::cache_latest): Likewise.
> > * testsuite/std/ranges/adaptors/cache_latest/1.cc: New test.
>
> The test is missing from the patch.
Whoops, below is the complete patch.
>
> > ---
> > libstdc++-v3/include/bits/version.def | 8 ++
> > libstdc++-v3/include/bits/version.h | 10 ++
> > libstdc++-v3/include/std/ranges | 189 ++++++++++++++++++++++++++
> > 3 files changed, 207 insertions(+)
> >
> > diff --git a/libstdc++-v3/include/bits/version.def
> > b/libstdc++-v3/include/bits/version.def
> > index 002e560dc0d..6fb5db2e1fc 100644
> > --- a/libstdc++-v3/include/bits/version.def
> > +++ b/libstdc++-v3/include/bits/version.def
> > @@ -1837,6 +1837,14 @@ ftms = {
> > };
> > };
> >
> > +ftms = {
> > + name = ranges_cache_latest;
> > + values = {
> > + v = 202411;
> > + cxxmin = 26;
> > + };
> > +};
> > +
> > ftms = {
> > name = ranges_concat;
> > values = {
> > diff --git a/libstdc++-v3/include/bits/version.h
> > b/libstdc++-v3/include/bits/version.h
> > index 70de189b1e0..db61a396c45 100644
> > --- a/libstdc++-v3/include/bits/version.h
> > +++ b/libstdc++-v3/include/bits/version.h
> > @@ -2035,6 +2035,16 @@
> > #endif /* !defined(__cpp_lib_is_virtual_base_of) &&
> > defined(__glibcxx_want_is_virtual_base_of) */
> > #undef __glibcxx_want_is_virtual_base_of
> >
> > +#if !defined(__cpp_lib_ranges_cache_latest)
> > +# if (__cplusplus > 202302L)
> > +# define __glibcxx_ranges_cache_latest 202411L
> > +# if defined(__glibcxx_want_all) ||
> > defined(__glibcxx_want_ranges_cache_latest)
> > +# define __cpp_lib_ranges_cache_latest 202411L
> > +# endif
> > +# endif
> > +#endif /* !defined(__cpp_lib_ranges_cache_latest) &&
> > defined(__glibcxx_want_ranges_cache_latest) */
> > +#undef __glibcxx_want_ranges_cache_latest
> > +
> > #if !defined(__cpp_lib_ranges_concat)
> > # if (__cplusplus > 202302L)
> > # define __glibcxx_ranges_concat 202403L
> > diff --git a/libstdc++-v3/include/std/ranges
> > b/libstdc++-v3/include/std/ranges
> > index 5c795a90fbc..db9a00be264 100644
> > --- a/libstdc++-v3/include/std/ranges
> > +++ b/libstdc++-v3/include/std/ranges
> > @@ -58,6 +58,7 @@
> > #define __glibcxx_want_ranges_as_const
> > #define __glibcxx_want_ranges_as_rvalue
> > #define __glibcxx_want_ranges_cartesian_product
> > +#define __glibcxx_want_ranges_cache_latest
> > #define __glibcxx_want_ranges_concat
> > #define __glibcxx_want_ranges_chunk
> > #define __glibcxx_want_ranges_chunk_by
> > @@ -1534,6 +1535,8 @@ namespace views::__adaptor
> > this->_M_payload._M_apply(_Optional_func{__f}, __i);
> > return this->_M_get();
> > }
> > +
> > + using _Optional_base<_Tp>::_M_reset;
I also forgot to mention this change in the ChangeLog.
> > };
> >
> > template<range _Range>
> > @@ -10203,6 +10206,192 @@ namespace ranges
> > } // namespace ranges
> > #endif // __cpp_lib_ranges_concat
> >
> > +#if __cpp_lib_ranges_cache_latest // C++ >= 26
> > +namespace ranges
> > +{
> > + template<input_range _Vp>
> > + requires view<_Vp>
> > + class cache_latest_view : public view_interface<cache_latest_view<_Vp>>
> > + {
> > + _Vp _M_base = _Vp();
> > +
> > + using __cache_t = conditional_t<is_reference_v<range_reference_t<_Vp>>,
> > + add_pointer_t<range_reference_t<_Vp>>,
> > + range_reference_t<_Vp>>;
>
> __conditional_t is cheaper to instantiate than conditional_t, so when
> it doesn't affect the mangled name of a public symbol we should prefer
> __conditional_t.
Ack, fixed below.
-- >8 --
libstdc++-v3/ChangeLog:
* include/bits/version.def (ranges_cache_latest): Define.
* include/bits/version.h: Regenerate.
* include/std/ranges (__detail::__non_propagating_cache::_M_reset):
Export from base class _Optional_base.
(cache_latest_view): Define for C++26.
(cache_latest_view::_Iterator): Likewise.
(cache_latest_view::_Sentinel): Likewise.
(views::__detail::__can_cache_latest): Likewise.
(views::_CacheLatest, views::cache_latest): Likewise.
* testsuite/std/ranges/adaptors/cache_latest/1.cc: New test.
---
libstdc++-v3/include/bits/version.def | 8 +
libstdc++-v3/include/bits/version.h | 10 +
libstdc++-v3/include/std/ranges | 189 ++++++++++++++++++
.../std/ranges/adaptors/cache_latest/1.cc | 72 +++++++
4 files changed, 279 insertions(+)
create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/cache_latest/1.cc
diff --git a/libstdc++-v3/include/bits/version.def
b/libstdc++-v3/include/bits/version.def
index 002e560dc0d..6fb5db2e1fc 100644
--- a/libstdc++-v3/include/bits/version.def
+++ b/libstdc++-v3/include/bits/version.def
@@ -1837,6 +1837,14 @@ ftms = {
};
};
+ftms = {
+ name = ranges_cache_latest;
+ values = {
+ v = 202411;
+ cxxmin = 26;
+ };
+};
+
ftms = {
name = ranges_concat;
values = {
diff --git a/libstdc++-v3/include/bits/version.h
b/libstdc++-v3/include/bits/version.h
index 70de189b1e0..db61a396c45 100644
--- a/libstdc++-v3/include/bits/version.h
+++ b/libstdc++-v3/include/bits/version.h
@@ -2035,6 +2035,16 @@
#endif /* !defined(__cpp_lib_is_virtual_base_of) &&
defined(__glibcxx_want_is_virtual_base_of) */
#undef __glibcxx_want_is_virtual_base_of
+#if !defined(__cpp_lib_ranges_cache_latest)
+# if (__cplusplus > 202302L)
+# define __glibcxx_ranges_cache_latest 202411L
+# if defined(__glibcxx_want_all) ||
defined(__glibcxx_want_ranges_cache_latest)
+# define __cpp_lib_ranges_cache_latest 202411L
+# endif
+# endif
+#endif /* !defined(__cpp_lib_ranges_cache_latest) &&
defined(__glibcxx_want_ranges_cache_latest) */
+#undef __glibcxx_want_ranges_cache_latest
+
#if !defined(__cpp_lib_ranges_concat)
# if (__cplusplus > 202302L)
# define __glibcxx_ranges_concat 202403L
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 5c795a90fbc..07ec90248a6 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -57,6 +57,7 @@
#define __glibcxx_want_ranges
#define __glibcxx_want_ranges_as_const
#define __glibcxx_want_ranges_as_rvalue
+#define __glibcxx_want_ranges_cache_latest
#define __glibcxx_want_ranges_cartesian_product
#define __glibcxx_want_ranges_concat
#define __glibcxx_want_ranges_chunk
@@ -1534,6 +1535,8 @@ namespace views::__adaptor
this->_M_payload._M_apply(_Optional_func{__f}, __i);
return this->_M_get();
}
+
+ using _Optional_base<_Tp>::_M_reset;
};
template<range _Range>
@@ -10203,6 +10206,192 @@ namespace ranges
} // namespace ranges
#endif // __cpp_lib_ranges_concat
+#if __cpp_lib_ranges_cache_latest // C++ >= 26
+namespace ranges
+{
+ template<input_range _Vp>
+ requires view<_Vp>
+ class cache_latest_view : public view_interface<cache_latest_view<_Vp>>
+ {
+ _Vp _M_base = _Vp();
+
+ using __cache_t = __conditional_t<is_reference_v<range_reference_t<_Vp>>,
+ add_pointer_t<range_reference_t<_Vp>>,
+ range_reference_t<_Vp>>;
+ __detail::__non_propagating_cache<__cache_t> _M_cache;
+
+ class _Iterator;
+ class _Sentinel;
+
+ public:
+ cache_latest_view() requires default_initializable<_Vp> = default;
+
+ constexpr explicit
+ cache_latest_view(_Vp __base)
+ : _M_base(std::move(__base))
+ { }
+
+ constexpr _Vp
+ base() const & requires copy_constructible<_Vp>
+ { return _M_base; }
+
+ constexpr _Vp
+ base() &&
+ { return std::move(_M_base); }
+
+ constexpr auto
+ begin()
+ { return _Iterator(*this); }
+
+ constexpr auto
+ end()
+ { return _Sentinel(*this); }
+
+ constexpr auto
+ size() requires sized_range<_Vp>
+ { return ranges::size(_M_base); }
+
+ constexpr auto
+ size() const requires sized_range<const _Vp>
+ { return ranges::size(_M_base); }
+ };
+
+ template<typename _Range>
+ cache_latest_view(_Range&&) -> cache_latest_view<views::all_t<_Range>>;
+
+ template<input_range _Vp>
+ requires view<_Vp>
+ class cache_latest_view<_Vp>::_Iterator
+ {
+ cache_latest_view* _M_parent;
+ iterator_t<_Vp> _M_current;
+
+ constexpr explicit
+ _Iterator(cache_latest_view& __parent)
+ : _M_parent(std::__addressof(__parent)),
+ _M_current(ranges::begin(__parent._M_base))
+ { }
+
+ friend class cache_latest_view;
+
+ public:
+ using difference_type = range_difference_t<_Vp>;
+ using value_type = range_value_t<_Vp>;
+ using iterator_concept = input_iterator_tag;
+
+ _Iterator(_Iterator&&) = default;
+
+ _Iterator&
+ operator=(_Iterator&&) = default;
+
+ constexpr iterator_t<_Vp>
+ base() &&
+ { return std::move(_M_current); }
+
+ constexpr const iterator_t<_Vp>&
+ base() const & noexcept
+ { return _M_current; }
+
+ constexpr range_reference_t<_Vp>&
+ operator*() const
+ {
+ if constexpr (is_reference_v<range_reference_t<_Vp>>)
+ {
+ if (!_M_parent->_M_cache)
+ _M_parent->_M_cache =
std::__addressof(__detail::__as_lvalue(*_M_current));
+ return **_M_parent->_M_cache;
+ }
+ else
+ {
+ if (!_M_parent->_M_cache)
+ _M_parent->_M_cache._M_emplace_deref(_M_current);
+ return *_M_parent->_M_cache;
+ }
+ }
+
+ constexpr _Iterator&
+ operator++()
+ {
+ _M_parent->_M_cache._M_reset();
+ ++_M_current;
+ return *this;
+ }
+
+ constexpr void
+ operator++(int)
+ { ++*this; }
+
+ friend constexpr range_rvalue_reference_t<_Vp>
+ iter_move(const _Iterator& __i)
+ noexcept(noexcept(ranges::iter_move(__i._M_current)))
+ { return ranges::iter_move(__i._M_current); }
+
+ friend constexpr void
+ iter_swap(const _Iterator& __x, const _Iterator& __y)
+ noexcept(noexcept(ranges::iter_swap(__x._M_current, __y._M_current)))
+ requires indirectly_swappable<iterator_t<_Vp>>
+ { ranges::iter_swap(__x._M_current, __y._M_current); }
+ };
+
+ template<input_range _Vp>
+ requires view<_Vp>
+ class cache_latest_view<_Vp>::_Sentinel
+ {
+ sentinel_t<_Vp> _M_end = sentinel_t<_Vp>();
+
+ constexpr explicit
+ _Sentinel(cache_latest_view& __parent)
+ : _M_end(ranges::end(__parent._M_base))
+ { }
+
+ friend class cache_latest_view;
+
+ public:
+ _Sentinel() = default;
+
+ constexpr sentinel_t<_Vp>
+ base() const
+ { return _M_end; }
+
+ friend constexpr bool
+ operator==(const _Iterator& __x, const _Sentinel& __y)
+ { return __x._M_current == __y._M_end; }
+
+ friend constexpr range_difference_t<_Vp>
+ operator-(const _Iterator& __x, const _Sentinel& __y)
+ requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
+ { return __x._M_current - __y._M_end; }
+
+ friend constexpr range_difference_t<_Vp>
+ operator-(const _Sentinel& __x, const _Iterator& __y)
+ requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
+ { return __x._M_end - __y._M_current; }
+ };
+
+ namespace views
+ {
+ namespace __detail
+ {
+ template<typename _Tp>
+ concept __can_cache_latest = requires {
cache_latest_view(std::declval<_Tp>()); };
+ }
+
+ struct _CacheLatest : __adaptor::_RangeAdaptorClosure<_CacheLatest>
+ {
+ template<viewable_range _Range>
+ requires __detail::__can_cache_latest<_Range>
+ constexpr auto
+ operator() [[nodiscard]] (_Range&& __r) const
+ { return cache_latest_view(std::forward<_Range>(__r)); }
+
+ static constexpr bool _S_has_simple_call_op = true;
+ };
+
+ inline constexpr _CacheLatest cache_latest;
+ }
+} // namespace ranges
+#endif // __cpp_lib_ranges_cache_latest
+
_GLIBCXX_END_NAMESPACE_VERSION
} // namespace std
#endif // library concepts
diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/cache_latest/1.cc
b/libstdc++-v3/testsuite/std/ranges/adaptors/cache_latest/1.cc
new file mode 100644
index 00000000000..5904831c4e0
--- /dev/null
+++ b/libstdc++-v3/testsuite/std/ranges/adaptors/cache_latest/1.cc
@@ -0,0 +1,72 @@
+// { dg-do run { target c++26 } }
+
+#include <ranges>
+
+#if __cpp_lib_ranges_cache_latest != 202411L
+# error "Feature-test macro __cpp_lib_ranges_cache_latest has wrong value in
<ranges>"
+#endif
+
+#include <algorithm>
+#include <testsuite_hooks.h>
+
+namespace ranges = std::ranges;
+namespace views = std::views;
+
+constexpr bool
+test01()
+{
+ int xs[] = {1,2,3,4,5};
+ auto v = xs | views::cache_latest;
+ VERIFY( ranges::equal(v, xs) );
+ VERIFY( ranges::size(v) == 5 );
+
+ auto it = v.begin();
+ auto st = v.end();
+ VERIFY( st - it == 5 );
+ VERIFY( it - st == -5 );
+ it++;
+ VERIFY( st - it == 4 );
+ VERIFY( it - st == -4 );
+
+ auto jt = v.begin();
+ ranges::iter_swap(it, jt);
+ VERIFY( ranges::equal(xs, (int[]){2,1,3,4,5}) );
+ int n = ranges::iter_move(it);
+ VERIFY( n == 1 );
+ ranges::iter_swap(it, jt);
+
+ auto w = views::iota(1, 6) | views::cache_latest;
+ VERIFY( ranges::equal(w, xs) );
+
+ return true;
+}
+
+constexpr bool
+test02()
+{
+ // Motivating example from P3138R5
+ int xs[] = {1, 2, 3, 4, 5};
+ int transform_count = 0;
+ auto v = xs | views::transform([&](int i){ ++transform_count; return i * i;
})
+ | views::filter([](int i){ return i % 2 == 0; });
+ VERIFY( ranges::equal(v, (int[]){4, 16}) );
+ VERIFY( transform_count == 7 );
+
+ transform_count = 0;
+ auto w = xs | views::transform([&](int i){ ++transform_count; return i * i;
})
+ | views::cache_latest
+ | views::filter([](int i){ return i % 2 == 0; });
+ VERIFY( ranges::equal(w, (int[]){4, 16}) );
+ VERIFY( transform_count == 5 );
+
+ return true;
+}
+
+int
+main()
+{
+ static_assert(test01());
+ static_assert(test02());
+ test01();
+ test02();
+}
--
2.48.1.329.ge2067b49ec.dirty
>
> > + __detail::__non_propagating_cache<__cache_t> _M_cache;
> > +
> > + class _Iterator;
> > + class _Sentinel;
> > +
> > + public:
> > + cache_latest_view() requires default_initializable<_Vp> = default;
> > +
> > + constexpr explicit
> > + cache_latest_view(_Vp __base)
> > + : _M_base(std::move(__base))
> > + { }
> > +
> > + constexpr _Vp
> > + base() const & requires copy_constructible<_Vp>
> > + { return _M_base; }
> > +
> > + constexpr _Vp
> > + base() &&
> > + { return std::move(_M_base); }
> > +
> > + constexpr auto
> > + begin()
> > + { return _Iterator(*this); }
> > +
> > + constexpr auto
> > + end()
> > + { return _Sentinel(*this); }
> > +
> > + constexpr auto
> > + size() requires sized_range<_Vp>
> > + { return ranges::size(_M_base); }
> > +
> > + constexpr auto
> > + size() const requires sized_range<const _Vp>
> > + { return ranges::size(_M_base); }
> > + };
> > +
> > + template<typename _Range>
> > + cache_latest_view(_Range&&) -> cache_latest_view<views::all_t<_Range>>;
> > +
> > + template<input_range _Vp>
> > + requires view<_Vp>
> > + class cache_latest_view<_Vp>::_Iterator
> > + {
> > + cache_latest_view* _M_parent;
> > + iterator_t<_Vp> _M_current;
> > +
> > + constexpr explicit
> > + _Iterator(cache_latest_view& __parent)
> > + : _M_parent(std::__addressof(__parent)),
> > + _M_current(ranges::begin(__parent._M_base))
> > + { }
> > +
> > + friend class cache_latest_view;
> > +
> > + public:
> > + using difference_type = range_difference_t<_Vp>;
> > + using value_type = range_value_t<_Vp>;
> > + using iterator_concept = input_iterator_tag;
> > +
> > + _Iterator(_Iterator&&) = default;
> > +
> > + _Iterator&
> > + operator=(_Iterator&&) = default;
> > +
> > + constexpr iterator_t<_Vp>
> > + base() &&
> > + { return std::move(_M_current); }
> > +
> > + constexpr const iterator_t<_Vp>&
> > + base() const & noexcept
> > + { return _M_current; }
> > +
> > + constexpr range_reference_t<_Vp>&
> > + operator*() const
> > + {
> > + if constexpr (is_reference_v<range_reference_t<_Vp>>)
> > + {
> > + if (!_M_parent->_M_cache)
> > + _M_parent->_M_cache =
> > std::__addressof(__detail::__as_lvalue(*_M_current));
> > + return **_M_parent->_M_cache;
> > + }
> > + else
> > + {
> > + if (!_M_parent->_M_cache)
> > + _M_parent->_M_cache._M_emplace_deref(_M_current);
> > + return *_M_parent->_M_cache;
> > + }
> > + }
> > +
> > + constexpr _Iterator&
> > + operator++()
> > + {
> > + _M_parent->_M_cache._M_reset();
> > + ++_M_current;
> > + return *this;
> > + }
> > +
> > + constexpr void
> > + operator++(int)
> > + { ++*this; }
> > +
> > + friend constexpr range_rvalue_reference_t<_Vp>
> > + iter_move(const _Iterator& __i)
> > + noexcept(noexcept(ranges::iter_move(__i._M_current)))
> > + { return ranges::iter_move(__i._M_current); }
> > +
> > + friend constexpr void
> > + iter_swap(const _Iterator& __x, const _Iterator& __y)
> > + noexcept(noexcept(ranges::iter_swap(__x._M_current, __y._M_current)))
> > + requires indirectly_swappable<iterator_t<_Vp>>
> > + { ranges::iter_swap(__x._M_current, __y._M_current); }
> > + };
> > +
> > + template<input_range _Vp>
> > + requires view<_Vp>
> > + class cache_latest_view<_Vp>::_Sentinel
> > + {
> > + sentinel_t<_Vp> _M_end = sentinel_t<_Vp>();
> > +
> > + constexpr explicit
> > + _Sentinel(cache_latest_view& parent)
> > + : _M_end(ranges::end(parent._M_base))
> > + { }
> > +
> > + friend class cache_latest_view;
> > +
> > + public:
> > + _Sentinel() = default;
> > +
> > + constexpr sentinel_t<_Vp>
> > + base() const
> > + { return _M_end; }
> > +
> > + friend constexpr bool
> > + operator==(const _Iterator& __x, const _Sentinel& __y)
> > + { return __x._M_current == __y._M_end; }
> > +
> > + friend constexpr range_difference_t<_Vp>
> > + operator-(const _Iterator& __x, const _Sentinel& __y)
> > + requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
> > + { return __x._M_current - __y._M_end; }
> > +
> > + friend constexpr range_difference_t<_Vp>
> > + operator-(const _Sentinel& __x, const _Iterator& __y)
> > + requires sized_sentinel_for<sentinel_t<_Vp>, iterator_t<_Vp>>
> > + { return __x._M_end - __y._M_current; }
> > + };
> > +
> > + namespace views
> > + {
> > + namespace __detail
> > + {
> > + template<typename _Tp>
> > + concept __can_cache_latest = requires {
> > cache_latest_view(std::declval<_Tp>()); };
> > + }
> > +
> > + struct _CacheLatest : __adaptor::_RangeAdaptorClosure<_CacheLatest>
> > + {
> > + template<viewable_range _Range>
> > + requires __detail::__can_cache_latest<_Range>
> > + constexpr auto
> > + operator() [[nodiscard]] (_Range&& __r) const
> > + { return cache_latest_view(std::forward<_Range>(__r)); }
> > +
> > + static constexpr bool _S_has_simple_call_op = true;
> > + };
> > +
> > + inline constexpr _CacheLatest cache_latest;
> > + }
> > +} // namespace ranges
> > +#endif // __cpp_lib_ranges_cache_latest
> > +
> > _GLIBCXX_END_NAMESPACE_VERSION
> > } // namespace std
> > #endif // library concepts
> > --
> > 2.48.1.291.g388218fac7.dirty
> >
>
>
