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libstdc++: Reuse _Bind_back_t functor in ranges::_Partial

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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>
Reviewed-by: Jonathan Wakely <jwakely@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>
This commit is contained in:
Tomasz Kamiński
2025-09-01 14:37:57 +02:00
parent b2adb7712c
commit 1a41e52d7e
2 changed files with 17 additions and 97 deletions
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10
libstdc++-v3/include/bits/binders.h
View File

@@ -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;
};

104
libstdc++-v3/include/std/ranges
View File

@@ -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;
};