[PATCH v2 3/3] ibstdc++: Reuse _Bind_back_t functor in ranges::_Partial
Tomasz Kamiński
tkaminsk@redhat.com
Thu Sep 4 08:58:13 GMT 2025
This patch refactors ranges::_Partial to be implemented using _Bind_back_t.
This allows it to benefit from the changes in r16-3398-g250dd5b5604fbc,
specifically making the closure trivially copyable. Since _Bind_back_t
already provides an optimized implementation for a single bound argument,
specializations for _Partial with a single argument are now removed.
We still preserve a specialization of _Partial for trivially copy-constructible
arguments that define only a const overload of operator(). To avoid
re-checking invocability constraints, this specialization calls the now-public,
unconstrained _Binder::_S_call static method instead of the constrained
_Binder::operator().
The primary specialization of _Partial retains its operator(), which
uses a simpler __adaptor_invocable constraint that does not consider
member pointers, as they are not relevant here. This implementation also
calls _Binder::_S_call to avoid re-performing overload resolution and
invocability checks for _Binder::operator().
Finally, the _M_binder member (_Bind_back_t) is now marked
[[no_unique_address]]. This is beneficial as ranges::_Partial is used with
ranges::to, which commonly has zero or empty bound arguments (e.g., stateless
allocators, comparators, or hash functions).
libstdc++-v3/ChangeLog:
* include/bits/binders.h (_Binder::_S_call): Make public.
* include/std/ranges (ranges::_Partial<_Adaptor, _Args...>):
Replace tuple<_Args...> with _Bind_back_t<_Adaptor, _Args...>.
(ranges::_Partial<_Adaptor, _Arg>): Remove.
Reviewed-by: Patrick Palka <ppalka@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
---
Tested on x86_64-linux locally. OK for trunk?
libstdc++-v3/include/bits/binders.h | 10 +--
libstdc++-v3/include/std/ranges | 104 ++++------------------------
2 files changed, 17 insertions(+), 97 deletions(-)
diff --git a/libstdc++-v3/include/bits/binders.h b/libstdc++-v3/include/bits/binders.h
index 08a330da6fe..f274389e5b4 100644
--- a/libstdc++-v3/include/bits/binders.h
+++ b/libstdc++-v3/include/bits/binders.h
@@ -186,11 +186,6 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
void operator()(_CallArgs&&...) const && = delete;
#endif
- private:
- using _BoundArgsStorage
- // _BoundArgs are required to be move-constructible, so this is valid.
- = decltype(__make_bound_args<_BoundArgs...>(std::declval<_BoundArgs>()...));
-
template<typename _Tp, typename... _CallArgs>
static constexpr
decltype(auto)
@@ -214,6 +209,11 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
std::forward<_CallArgs>(__call_args)...);
}
+ private:
+ using _BoundArgsStorage
+ // _BoundArgs are required to be move-constructible, so this is valid.
+ = decltype(__make_bound_args<_BoundArgs...>(std::declval<_BoundArgs>()...));
+
[[no_unique_address]] _Fd _M_fd;
[[no_unique_address]] _BoundArgsStorage _M_bound_args;
};
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 2970b2cbe00..98154a02e9e 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -51,6 +51,7 @@
#include <utility>
#include <variant>
#endif
+#include <bits/binders.h>
#include <bits/ranges_util.h>
#include <bits/refwrap.h>
@@ -1047,14 +1048,15 @@ namespace views::__adaptor
template<typename _Adaptor, typename... _Args>
struct _Partial : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>>
{
- tuple<_Args...> _M_args;
+ using _Binder = _Bind_back_t<_Adaptor, _Args...>;
+ [[no_unique_address]] _Binder _M_binder;
// First parameter is to ensure this constructor is never used
// instead of the copy/move constructor.
template<typename... _Ts>
constexpr
_Partial(int, _Ts&&... __args)
- : _M_args(std::forward<_Ts>(__args)...)
+ : _M_binder(0, _Adaptor(), std::forward<_Ts>(__args)...)
{ }
// Invoke _Adaptor with arguments __r, _M_args... according to the
@@ -1065,75 +1067,21 @@ namespace views::__adaptor
constexpr auto
operator()(this _Self&& __self, _Range&& __r)
{
- auto __forwarder = [&__r] (auto&&... __args) {
- return _Adaptor{}(std::forward<_Range>(__r),
- std::forward<decltype(__args)>(__args)...);
- };
- return std::apply(__forwarder, __like_t<_Self, _Partial>(__self)._M_args);
+ return _Binder::_S_call(__like_t<_Self, _Partial>(__self)._M_binder,
+ std::forward<_Range>(__r));
}
#else
template<typename _Range>
requires __adaptor_invocable<_Adaptor, _Range, const _Args&...>
constexpr auto
operator()(_Range&& __r) const &
- {
- auto __forwarder = [&__r] (const auto&... __args) {
- return _Adaptor{}(std::forward<_Range>(__r), __args...);
- };
- return std::apply(__forwarder, _M_args);
- }
+ { return _Binder::_S_call(_M_binder, std::forward<_Range>(__r)); }
template<typename _Range>
requires __adaptor_invocable<_Adaptor, _Range, _Args...>
constexpr auto
operator()(_Range&& __r) &&
- {
- auto __forwarder = [&__r] (auto&... __args) {
- return _Adaptor{}(std::forward<_Range>(__r), std::move(__args)...);
- };
- return std::apply(__forwarder, _M_args);
- }
-
- template<typename _Range>
- constexpr auto
- operator()(_Range&& __r) const && = delete;
-#endif
- };
-
- // A lightweight specialization of the above primary template for
- // the common case where _Adaptor accepts a single extra argument.
- template<typename _Adaptor, typename _Arg>
- struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>>
- {
- _Arg _M_arg;
-
- template<typename _Tp>
- constexpr
- _Partial(int, _Tp&& __arg)
- : _M_arg(std::forward<_Tp>(__arg))
- { }
-
-#if __cpp_explicit_this_parameter
- template<typename _Self, typename _Range>
- requires __adaptor_invocable<_Adaptor, _Range, __like_t<_Self, _Arg>>
- constexpr auto
- operator()(this _Self&& __self, _Range&& __r)
- {
- return _Adaptor{}(std::forward<_Range>(__r),
- __like_t<_Self, _Partial>(__self)._M_arg);
- }
-#else
- template<typename _Range>
- requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
- constexpr auto
- operator()(_Range&& __r) const &
- { return _Adaptor{}(std::forward<_Range>(__r), _M_arg); }
-
- template<typename _Range>
- requires __adaptor_invocable<_Adaptor, _Range, _Arg>
- constexpr auto
- operator()(_Range&& __r) &&
- { return _Adaptor{}(std::forward<_Range>(__r), std::move(_M_arg)); }
+ { return _Binder::_S_call(std::move(_M_binder), std::forward<_Range>(__r)); }
template<typename _Range>
constexpr auto
@@ -1150,12 +1098,13 @@ namespace views::__adaptor
&& (is_trivially_copy_constructible_v<_Args> && ...)
struct _Partial<_Adaptor, _Args...> : _RangeAdaptorClosure<_Partial<_Adaptor, _Args...>>
{
- tuple<_Args...> _M_args;
+ using _Binder = _Bind_back_t<_Adaptor, _Args...>;
+ [[no_unique_address]] _Binder _M_binder;
template<typename... _Ts>
constexpr
_Partial(int, _Ts&&... __args)
- : _M_args(std::forward<_Ts>(__args)...)
+ : _M_binder(0, _Adaptor(), std::forward<_Ts>(__args)...)
{ }
// Invoke _Adaptor with arguments __r, const _M_args&... regardless
@@ -1164,36 +1113,7 @@ namespace views::__adaptor
requires __adaptor_invocable<_Adaptor, _Range, const _Args&...>
constexpr auto
operator()(_Range&& __r) const
- {
- auto __forwarder = [&__r] (const auto&... __args) {
- return _Adaptor{}(std::forward<_Range>(__r), __args...);
- };
- return std::apply(__forwarder, _M_args);
- }
-
- static constexpr bool _S_has_simple_call_op = true;
- };
-
- // A lightweight specialization of the above template for the common case
- // where _Adaptor accepts a single extra argument.
- template<typename _Adaptor, typename _Arg>
- requires __adaptor_has_simple_extra_args<_Adaptor, _Arg>
- && is_trivially_copy_constructible_v<_Arg>
- struct _Partial<_Adaptor, _Arg> : _RangeAdaptorClosure<_Partial<_Adaptor, _Arg>>
- {
- _Arg _M_arg;
-
- template<typename _Tp>
- constexpr
- _Partial(int, _Tp&& __arg)
- : _M_arg(std::forward<_Tp>(__arg))
- { }
-
- template<typename _Range>
- requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
- constexpr auto
- operator()(_Range&& __r) const
- { return _Adaptor{}(std::forward<_Range>(__r), _M_arg); }
+ { return _Binder::_S_call(_M_binder, std::forward<_Range>(__r)); }
static constexpr bool _S_has_simple_call_op = true;
};
--
2.51.0
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