G++ implements P1972R2 since r11-1597-0ca22d027ecc and so we no longer
need the P0608R3 special case to prevent narrowing conversions to bool.
Since non-GNU compilers don't necessarily implment P1972R2 yet, this
may cause a regression for those compilers. There is no feature-test
macro we can use to detect it though, so we'll have to live with it.
libstdc++-v3/ChangeLog:
PR libstdc++/95832
* include/std/variant (__detail::__variant::_Build_FUN): Remove
partial specialization to prevent narrowing conversions to bool.
* testsuite/20_util/variant/compile.cc: Test non-narrowing
conversions to bool.
* testsuite/20_util/variant/run.cc: Likewise.
Tested powerpc64le-linux, committed to master.
Not possible to backport to gcc-10, because the front end support
isn't there. That unfortunately means std::variant construction works
differently in each of gcc-9, gcc-10 and master.
commit c98fc4eb3afeda6ad8220d0d79bc1247a92c7c65
Author: Jonathan Wakely <jwak...@redhat.com>
Date: Tue Jun 23 10:24:49 2020 +0100
libstdc++: Implement P1972R2 changes to std::variant (PR 95832)
G++ implements P1972R2 since r11-1597-0ca22d027ecc and so we no longer
need the P0608R3 special case to prevent narrowing conversions to bool.
Since non-GNU compilers don't necessarily implment P1972R2 yet, this
may cause a regression for those compilers. There is no feature-test
macro we can use to detect it though, so we'll have to live with it.
libstdc++-v3/ChangeLog:
PR libstdc++/95832
* include/std/variant (__detail::__variant::_Build_FUN): Remove
partial specialization to prevent narrowing conversions to bool.
* testsuite/20_util/variant/compile.cc: Test non-narrowing
conversions to bool.
* testsuite/20_util/variant/run.cc: Likewise.
diff --git a/libstdc++-v3/include/std/variant b/libstdc++-v3/include/std/variant
index 258a5fb18bd..6eeb3c80ec2 100644
--- a/libstdc++-v3/include/std/variant
+++ b/libstdc++-v3/include/std/variant
@@ -164,7 +164,7 @@ namespace __detail
{
namespace __variant
{
- // Returns the first appearence of _Tp in _Types.
+ // Returns the first appearance of _Tp in _Types.
// Returns sizeof...(_Types) if _Tp is not in _Types.
template<typename _Tp, typename... _Types>
struct __index_of : std::integral_constant<size_t, 0> {};
@@ -733,10 +733,8 @@ namespace __variant
// Helper used to check for valid conversions that don't involve narrowing.
template<typename _Ti> struct _Arr { _Ti _M_x[1]; };
- // Build an imaginary function FUN(Ti) for each alternative type Ti
- template<size_t _Ind, typename _Tp, typename _Ti,
- bool _Ti_is_cv_bool = is_same_v<remove_cv_t<_Ti>, bool>,
- typename = void>
+ // "Build an imaginary function FUN(Ti) for each alternative type Ti"
+ template<size_t _Ind, typename _Tp, typename _Ti, typename = void>
struct _Build_FUN
{
// This function means 'using _Build_FUN<I, T, Ti>::_S_fun;' is valid,
@@ -744,24 +742,15 @@ namespace __variant
void _S_fun();
};
- // ... for which Ti x[] = {std::forward<T>(t)}; is well-formed,
+ // "... for which Ti x[] = {std::forward<T>(t)}; is well-formed."
template<size_t _Ind, typename _Tp, typename _Ti>
- struct _Build_FUN<_Ind, _Tp, _Ti, false,
+ struct _Build_FUN<_Ind, _Tp, _Ti,
void_t<decltype(_Arr<_Ti>{{std::declval<_Tp>()}})>>
{
// This is the FUN function for type _Ti, with index _Ind
static integral_constant<size_t, _Ind> _S_fun(_Ti);
};
- // ... and if Ti is cv bool, remove_cvref_t<T> is bool.
- template<size_t _Ind, typename _Tp, typename _Ti>
- struct _Build_FUN<_Ind, _Tp, _Ti, true,
- enable_if_t<is_same_v<__remove_cvref_t<_Tp>, bool>>>
- {
- // This is the FUN function for when _Ti is cv bool, with index _Ind
- static integral_constant<size_t, _Ind> _S_fun(_Ti);
- };
-
template<typename _Tp, typename _Variant,
typename = make_index_sequence<variant_size_v<_Variant>>>
struct _Build_FUNs;
diff --git a/libstdc++-v3/testsuite/20_util/variant/compile.cc
b/libstdc++-v3/testsuite/20_util/variant/compile.cc
index a53071c8867..b2b60d1cf10 100644
--- a/libstdc++-v3/testsuite/20_util/variant/compile.cc
+++ b/libstdc++-v3/testsuite/20_util/variant/compile.cc
@@ -155,6 +155,14 @@ void arbitrary_ctor()
static_assert(!is_constructible_v<variant<int>, unsigned>);
static_assert(!is_constructible_v<variant<bool>, int>);
static_assert(!is_constructible_v<variant<bool>, void*>);
+
+ // P1957R2 Converting from T* to bool should be considered narrowing
+ struct ConvertibleToBool
+ {
+ operator bool() const { return true; }
+ };
+ static_assert(is_constructible_v<variant<bool>, ConvertibleToBool>);
+ static_assert(is_constructible_v<variant<bool, int>, ConvertibleToBool>);
}
struct none { none() = delete; };
diff --git a/libstdc++-v3/testsuite/20_util/variant/run.cc
b/libstdc++-v3/testsuite/20_util/variant/run.cc
index 3e2228a4666..0ac5de25289 100644
--- a/libstdc++-v3/testsuite/20_util/variant/run.cc
+++ b/libstdc++-v3/testsuite/20_util/variant/run.cc
@@ -139,6 +139,20 @@ void arbitrary_ctor()
variant<float, big_int> v3 = 0;
VERIFY(v3.index() == 1);
}
+
+ {
+ // P1957R2 Converting from T* to bool should be considered narrowing
+ struct ConvertibleToBool
+ {
+ operator bool() const { return true; }
+ };
+ variant<bool> v1 = ConvertibleToBool();
+ VERIFY(std::get<0>(v1) == true);
+ variant<bool, int> v2 = ConvertibleToBool();
+ VERIFY(std::get<0>(v2) == true);
+ variant<int, bool> v3 = ConvertibleToBool();
+ VERIFY(std::get<1>(v3) == true);
+ }
}
struct ThrowingMoveCtorThrowsCopyCtor
@@ -226,6 +240,23 @@ void arbitrary_assign()
v3 = 0;
VERIFY(v3.index() == 1);
}
+
+ {
+ // P1957R2 Converting from T* to bool should be considered narrowing
+ struct ConvertibleToBool
+ {
+ operator bool() const { return true; }
+ };
+ variant<bool> v1;
+ v1 = ConvertibleToBool();
+ VERIFY(std::get<0>(v1) == true);
+ variant<bool, int> v2;
+ v2 = ConvertibleToBool();
+ VERIFY(std::get<0>(v2) == true);
+ variant<int, bool> v3;
+ v3 = ConvertibleToBool();
+ VERIFY(std::get<1>(v3) == true);
+ }
}
void dtor()
