[PATCH] libstdc++: fix uses of explicit object parameter [PR116038]
Jonathan Wakely
jwakely@redhat.com
Thu Jul 25 10:51:33 GMT 2024
On Thu, 25 Jul 2024 at 01:04, Patrick Palka <ppalka@redhat.com> wrote:
>
> Tested on x86_64-pc-linux-gnu, does this look OK for trunk/14 (after
> 14.2 is released)?
Yes to both, thanks.
>
> -- >8 --
>
> The type of an implicit object parameter is always the current class.
> For an explicit object parameter however, its deduced type can be a
> class derived from the current class. So when combining multiple
> implicit-object overloads into a single explicit-object overload we need
> to account for this possibility. For example, when accessing a member
> from the current class through an explicit object parameter, it may be a
> derived class from which the member is not accessible, as in the below
> testcases.
>
> This pitfall is discussed[1] in the deducing this paper. The general
> solution is to cast the explicit object parameter to (a reference to)
> the current class, appropriately qualified, rather than e.g. using
> std::forward which preserves the deduced type.
>
> This patch corrects the existing problematic uses of explicit object
> parameters in the library, all of which forward the parameter via
> std::forward, to instead cast the parameter to the current class via
> our __like_t alias template. Note that unlike the paper's like_t,
> ours always returns a reference so when can just write
>
> __like_t<Self, B>(self)
>
> instead of
>
> (_like_t<Self, B>&&)self
>
> as the paper does.
>
> [1]: https://wg21.link/P0847#name-lookup-within-member-functions and the
> section after that
>
> PR libstdc++/116038
>
> libstdc++-v3/ChangeLog:
>
> * include/std/functional (_Bind_front::operator()): Use __like_t
> instead of std::forward when forwarding __self.
> (_Bind_back::operator()): Likewise.
> * include/std/ranges (_Partial::operator()): Likewise.
> (_Pipe::operator()): Likewise.
> * testsuite/20_util/function_objects/bind_back/116038.cc: New test.
> * testsuite/20_util/function_objects/bind_front/116038.cc: New test.
> * testsuite/std/ranges/adaptors/116038.cc: New test.
> ---
> libstdc++-v3/include/std/functional | 4 +--
> libstdc++-v3/include/std/ranges | 11 ++++---
> .../function_objects/bind_back/116038.cc | 27 +++++++++++++++++
> .../function_objects/bind_front/116038.cc | 27 +++++++++++++++++
> .../testsuite/std/ranges/adaptors/116038.cc | 29 +++++++++++++++++++
> 5 files changed, 92 insertions(+), 6 deletions(-)
> create mode 100644 libstdc++-v3/testsuite/20_util/function_objects/bind_back/116038.cc
> create mode 100644 libstdc++-v3/testsuite/20_util/function_objects/bind_front/116038.cc
> create mode 100644 libstdc++-v3/testsuite/std/ranges/adaptors/116038.cc
>
> diff --git a/libstdc++-v3/include/std/functional b/libstdc++-v3/include/std/functional
> index 99364286a72..7788a963757 100644
> --- a/libstdc++-v3/include/std/functional
> +++ b/libstdc++-v3/include/std/functional
> @@ -944,7 +944,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<__like_t<_Self, _Fd>,
> __like_t<_Self, _BoundArgs>..., _CallArgs...>)
> {
> - return _S_call(std::forward<_Self>(__self), _BoundIndices(),
> + return _S_call(__like_t<_Self, _Bind_front>(__self), _BoundIndices(),
> std::forward<_CallArgs>(__call_args)...);
> }
> #else
> @@ -1072,7 +1072,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
> noexcept(is_nothrow_invocable_v<__like_t<_Self, _Fd>,
> _CallArgs..., __like_t<_Self, _BoundArgs>...>)
> {
> - return _S_call(std::forward<_Self>(__self), _BoundIndices(),
> + return _S_call(__like_t<_Self, _Bind_back>(__self), _BoundIndices(),
> std::forward<_CallArgs>(__call_args)...);
> }
>
> diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
> index 3f335b95a08..b7c7aa36ddc 100644
> --- a/libstdc++-v3/include/std/ranges
> +++ b/libstdc++-v3/include/std/ranges
> @@ -1033,7 +1033,7 @@ namespace views::__adaptor
> return _Adaptor{}(std::forward<_Range>(__r),
> std::forward<decltype(__args)>(__args)...);
> };
> - return std::apply(__forwarder, std::forward<_Self>(__self)._M_args);
> + return std::apply(__forwarder, __like_t<_Self, _Partial>(__self)._M_args);
> }
> #else
> template<typename _Range>
> @@ -1082,7 +1082,10 @@ namespace views::__adaptor
> requires __adaptor_invocable<_Adaptor, _Range, __like_t<_Self, _Arg>>
> constexpr auto
> operator()(this _Self&& __self, _Range&& __r)
> - { return _Adaptor{}(std::forward<_Range>(__r), std::forward<_Self>(__self)._M_arg); }
> + {
> + return _Adaptor{}(std::forward<_Range>(__r),
> + __like_t<_Self, _Partial>(__self)._M_arg);
> + }
> #else
> template<typename _Range>
> requires __adaptor_invocable<_Adaptor, _Range, const _Arg&>
> @@ -1185,8 +1188,8 @@ namespace views::__adaptor
> constexpr auto
> operator()(this _Self&& __self, _Range&& __r)
> {
> - return (std::forward<_Self>(__self)._M_rhs
> - (std::forward<_Self>(__self)._M_lhs
> + return (__like_t<_Self, _Pipe>(__self)._M_rhs
> + (__like_t<_Self, _Pipe>(__self)._M_lhs
> (std::forward<_Range>(__r))));
> }
> #else
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_back/116038.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/116038.cc
> new file mode 100644
> index 00000000000..ed392b1434e
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_back/116038.cc
> @@ -0,0 +1,27 @@
> +// PR libstdc++/116038
> +// { dg-do compile { target c++23 } }
> +
> +#include <functional>
> +#include <utility>
> +
> +struct A { };
> +struct B { };
> +
> +template<class... Ts>
> +struct overloaded : private Ts... {
> + overloaded(Ts...);
> + using Ts::operator()...;
> +};
> +
> +int apply_a(A, int);
> +int apply_b(B, int);
> +
> +int main() {
> + overloaded o = { std::bind_back(apply_a, 1),
> + std::bind_back(apply_b, 2) };
> + A a;
> + o(a);
> + std::as_const(o)(a);
> + std::move(o)(a);
> + std::move(std::as_const(o))(a);
> +}
> diff --git a/libstdc++-v3/testsuite/20_util/function_objects/bind_front/116038.cc b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/116038.cc
> new file mode 100644
> index 00000000000..3bf1226375b
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/20_util/function_objects/bind_front/116038.cc
> @@ -0,0 +1,27 @@
> +// PR libstdc++/116038
> +// { dg-do compile { target c++20 } }
> +
> +#include <functional>
> +#include <utility>
> +
> +struct A { };
> +struct B { };
> +
> +template<class... Ts>
> +struct overloaded : private Ts... {
> + overloaded(Ts...);
> + using Ts::operator()...;
> +};
> +
> +int apply_a(int, A);
> +int apply_b(int, B);
> +
> +int main() {
> + overloaded o = { std::bind_front(apply_a, 1),
> + std::bind_front(apply_b, 2) };
> + A a;
> + o(a);
> + std::as_const(o)(a);
> + std::move(o)(a);
> + std::move(std::as_const(o))(a);
> +}
> diff --git a/libstdc++-v3/testsuite/std/ranges/adaptors/116038.cc b/libstdc++-v3/testsuite/std/ranges/adaptors/116038.cc
> new file mode 100644
> index 00000000000..1afdf3d06d1
> --- /dev/null
> +++ b/libstdc++-v3/testsuite/std/ranges/adaptors/116038.cc
> @@ -0,0 +1,29 @@
> +// PR libstdc++/116038
> +// { dg-do compile { target c++20 } }
> +
> +#include <ranges>
> +#include <utility>
> +
> +struct A { };
> +struct B { };
> +
> +template<class... Ts>
> +struct overloaded : private Ts... {
> + overloaded(Ts...);
> + using Ts::operator()...;
> +};
> +
> +int x[5];
> +struct integralish { operator int() const; } i;
> +
> +int main() {
> + overloaded o1 = { std::views::drop(i) };
> + o1(x);
> + std::move(o1)(x);
> + std::as_const(o1)(x);
> +
> + overloaded o2 = { std::views::drop(i) | std::views::take(i) };
> + o2(x);
> + std::move(o2)(x);
> + std::as_const(o1)(x);
> +}
> --
> 2.46.0.rc2
>
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