[gcc r12-220] libstdc++: Deprecate non-standard std::pair constructors [PR 99957]
Jonathan Wakely
redi@gcc.gnu.org
Wed Apr 28 16:57:00 GMT 2021
https://gcc.gnu.org/g:d96db15967e78d7cecea3b1cf3169ceb924678ac
commit r12-220-gd96db15967e78d7cecea3b1cf3169ceb924678ac
Author: Jonathan Wakely <jwakely@redhat.com>
Date: Wed Apr 28 17:46:01 2021 +0100
libstdc++: Deprecate non-standard std::pair constructors [PR 99957]
This deprecates the non-standard std::pair constructors that support
construction from an rvalue and a literal zero used as a null pointer
constant. We can't just add the deprecated attribute to those
constructors, because they're currently used by correct code when they
are a better match than the constructors required by the standard e.g.
int i = 0;
const int j = 0;
std::pair<int, int> p(i, j); // uses pair(U1&&, const int&)
This patch adjusts the parameter types and constraints of those
constructors so that they only get used for literal zeros, and the
pair(U1&&, U2&&) constructor gets used otherwise. Once they're only used
for initializations that should be ill-formed we can add the deprecated
attribute.
The deprecated attribute is used to suggest that the user code uses
nullptr, which avoids the problem of 0 deducing as int instead of a null
pointer constant.
libstdc++-v3/ChangeLog:
PR libstdc++/99957
* include/bits/stl_pair.h (_PCC::_MoveCopyPair, _PCC::_CopyMovePair):
Combine and replace with ...
(_PCC::_DeprConsPair): New SFINAE helper function.
(pair): Merge preprocessor blocks so that all C++03 members
are defined together at the end.
(pair::pair(const _T1&, _U2&&), pair::pair(_U1&&, const _T2&)):
Replace _T1 and _T2 parameters with __null_ptr_constant and
adjust constraints.
* testsuite/20_util/pair/40925.cc: Use nullptr instead of 0.
* testsuite/20_util/pair/cons/explicit_construct.cc: Likewise.
* testsuite/20_util/pair/cons/99957.cc: New test.
Diff:
---
libstdc++-v3/include/bits/stl_pair.h | 151 ++++++++++++---------
libstdc++-v3/testsuite/20_util/pair/40925.cc | 14 +-
libstdc++-v3/testsuite/20_util/pair/cons/99957.cc | 28 ++++
.../20_util/pair/cons/explicit_construct.cc | 8 +-
4 files changed, 124 insertions(+), 77 deletions(-)
diff --git a/libstdc++-v3/include/bits/stl_pair.h b/libstdc++-v3/include/bits/stl_pair.h
index 70262f9508f..883d7441b3d 100644
--- a/libstdc++-v3/include/bits/stl_pair.h
+++ b/libstdc++-v3/include/bits/stl_pair.h
@@ -128,34 +128,21 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
is_convertible<_U2&&, _T2>>::value;
}
- template <bool __implicit, typename _U1, typename _U2>
- static constexpr bool _CopyMovePair()
- {
- using __do_converts = __and_<is_convertible<const _U1&, _T1>,
- is_convertible<_U2&&, _T2>>;
- using __converts = typename conditional<__implicit,
- __do_converts,
- __not_<__do_converts>>::type;
- return __and_<is_constructible<_T1, const _U1&>,
- is_constructible<_T2, _U2&&>,
- __converts
- >::value;
- }
template <bool __implicit, typename _U1, typename _U2>
- static constexpr bool _MoveCopyPair()
+ static constexpr bool _DeprConsPair()
{
using __do_converts = __and_<is_convertible<_U1&&, _T1>,
- is_convertible<const _U2&, _T2>>;
+ is_convertible<_U2&&, _T2>>;
using __converts = typename conditional<__implicit,
- __do_converts,
- __not_<__do_converts>>::type;
+ __do_converts,
+ __not_<__do_converts>>::type;
return __and_<is_constructible<_T1, _U1&&>,
- is_constructible<_T2, const _U2&&>,
+ is_constructible<_T2, _U2&&>,
__converts
- >::value;
+ >::value;
}
- };
+ };
template <typename _T1, typename _T2>
struct _PCC<false, _T1, _T2>
@@ -183,7 +170,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
{
return false;
}
- };
+ };
#endif // C++11
template<typename _U1, typename _U2> class __pair_base
@@ -217,22 +204,20 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_T1 first; ///< The first member
_T2 second; ///< The second member
- // _GLIBCXX_RESOLVE_LIB_DEFECTS
- // 265. std::pair::pair() effects overly restrictive
+#if __cplusplus >= 201103L
+ // C++11 (and later) implementation.
+
/** The default constructor creates @c first and @c second using their
* respective default constructors. */
-#if __cplusplus >= 201103L
template <typename _U1 = _T1,
typename _U2 = _T2,
typename enable_if<__and_<
__is_implicitly_default_constructible<_U1>,
__is_implicitly_default_constructible<_U2>>
::value, bool>::type = true>
-#endif
- _GLIBCXX_CONSTEXPR pair()
+ constexpr pair()
: first(), second() { }
-#if __cplusplus >= 201103L
template <typename _U1 = _T1,
typename _U2 = _T2,
typename enable_if<__and_<
@@ -244,13 +229,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
::value, bool>::type = false>
explicit constexpr pair()
: first(), second() { }
-#endif
-#if __cplusplus < 201103L
- /// Two objects may be passed to a @c pair constructor to be copied.
- pair(const _T1& __a, const _T2& __b)
- : first(__a), second(__b) { }
-#else
// Shortcut for constraining the templates that don't take pairs.
/// @cond undocumented
using _PCCP = _PCC<true, _T1, _T2>;
@@ -275,14 +254,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool>::type=false>
explicit constexpr pair(const _T1& __a, const _T2& __b)
: first(__a), second(__b) { }
-#endif
-#if __cplusplus < 201103L
- /// There is also a templated constructor to convert from other pairs.
- template<typename _U1, typename _U2>
- pair(const pair<_U1, _U2>& __p)
- : first(__p.first), second(__p.second) { }
-#else
// Shortcut for constraining the templates that take pairs.
/// @cond undocumented
template <typename _U1, typename _U2>
@@ -308,40 +280,68 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
bool>::type=false>
explicit constexpr pair(const pair<_U1, _U2>& __p)
: first(__p.first), second(__p.second) { }
-#endif
-#if __cplusplus >= 201103L
constexpr pair(const pair&) = default; ///< Copy constructor
constexpr pair(pair&&) = default; ///< Move constructor
- // DR 811.
- template<typename _U1, typename
- enable_if<_PCCP::template
- _MoveCopyPair<true, _U1, _T2>(),
- bool>::type=true>
- constexpr pair(_U1&& __x, const _T2& __y)
- : first(std::forward<_U1>(__x)), second(__y) { }
+#if _GLIBCXX_USE_DEPRECATED
+ private:
+ /// @cond undocumented
- template<typename _U1, typename
- enable_if<_PCCP::template
- _MoveCopyPair<false, _U1, _T2>(),
- bool>::type=false>
- explicit constexpr pair(_U1&& __x, const _T2& __y)
- : first(std::forward<_U1>(__x)), second(__y) { }
+ // A type which can be constructed from literal zero, but not nullptr
+ struct __null_ptr_constant
+ {
+ __null_ptr_constant(int __null_ptr_constant::*) { }
+ template<typename _Tp,
+ typename = __enable_if_t<is_null_pointer<_Tp>::value>>
+ __null_ptr_constant(_Tp) = delete;
+ };
- template<typename _U2, typename
- enable_if<_PCCP::template
- _CopyMovePair<true, _T1, _U2>(),
- bool>::type=true>
- constexpr pair(const _T1& __x, _U2&& __y)
- : first(__x), second(std::forward<_U2>(__y)) { }
+ // True if type _Up is one of _Tp& or const _Tp&
+ template<typename _Up, typename _Tp>
+ using __is_lvalue_of
+ = __or_<is_same<_Up, const _Tp&>, is_same<_Up, _Tp&>>;
- template<typename _U2, typename
- enable_if<_PCCP::template
- _CopyMovePair<false, _T1, _U2>(),
- bool>::type=false>
- explicit pair(const _T1& __x, _U2&& __y)
- : first(__x), second(std::forward<_U2>(__y)) { }
+ /// @endcond
+ public:
+
+ // Deprecated extensions to DR 811.
+ template<typename _U1,
+ __enable_if_t<!__is_lvalue_of<_U1, _T1>::value
+ && _PCCP::template
+ _DeprConsPair<true, _U1, nullptr_t>(),
+ bool> = true>
+ _GLIBCXX_DEPRECATED_SUGGEST("nullptr")
+ constexpr pair(_U1&& __x, __null_ptr_constant)
+ : first(std::forward<_U1>(__x)), second(nullptr) { }
+
+ template<typename _U1,
+ __enable_if_t<!__is_lvalue_of<_U1, _T1>::value
+ && _PCCP::template
+ _DeprConsPair<false, _U1, nullptr_t>(),
+ bool> = false>
+ _GLIBCXX_DEPRECATED_SUGGEST("nullptr")
+ explicit constexpr pair(_U1&& __x, __null_ptr_constant)
+ : first(std::forward<_U1>(__x)), second(nullptr) { }
+
+ template<typename _U2,
+ __enable_if_t<!__is_lvalue_of<_U2, _T2>::value
+ && _PCCP::template
+ _DeprConsPair<true, nullptr_t, _U2>(),
+ bool> = true>
+ _GLIBCXX_DEPRECATED_SUGGEST("nullptr")
+ constexpr pair(__null_ptr_constant, _U2&& __y)
+ : first(nullptr), second(std::forward<_U2>(__y)) { }
+
+ template<typename _U2,
+ __enable_if_t<!__is_lvalue_of<_U2, _T2>::value
+ && _PCCP::template
+ _DeprConsPair<false, nullptr_t, _U2>(),
+ bool> = false>
+ _GLIBCXX_DEPRECATED_SUGGEST("nullptr")
+ explicit pair(__null_ptr_constant, _U2&& __y)
+ : first(nullptr), second(std::forward<_U2>(__y)) { }
+#endif // _GLIBCXX_USE_DEPRECATED
template<typename _U1, typename _U2, typename
enable_if<_PCCP::template
@@ -451,6 +451,23 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
_GLIBCXX20_CONSTEXPR
pair(tuple<_Args1...>&, tuple<_Args2...>&,
_Index_tuple<_Indexes1...>, _Index_tuple<_Indexes2...>);
+#else
+ // C++03 implementation
+
+ // _GLIBCXX_RESOLVE_LIB_DEFECTS
+ // 265. std::pair::pair() effects overly restrictive
+ /** The default constructor creates @c first and @c second using their
+ * respective default constructors. */
+ pair() : first(), second() { }
+
+ /// Two objects may be passed to a `pair` constructor to be copied.
+ pair(const _T1& __a, const _T2& __b)
+ : first(__a), second(__b) { }
+
+ /// Templated constructor to convert from other pairs.
+ template<typename _U1, typename _U2>
+ pair(const pair<_U1, _U2>& __p)
+ : first(__p.first), second(__p.second) { }
#endif // C++11
};
diff --git a/libstdc++-v3/testsuite/20_util/pair/40925.cc b/libstdc++-v3/testsuite/20_util/pair/40925.cc
index 157bef621be..c95cb380b18 100644
--- a/libstdc++-v3/testsuite/20_util/pair/40925.cc
+++ b/libstdc++-v3/testsuite/20_util/pair/40925.cc
@@ -20,7 +20,7 @@
#include <utility>
struct X
-{
+{
explicit X(int, int) { }
private:
@@ -36,7 +36,7 @@ private:
move_only(const move_only&) = delete;
};
-// libstdc++/40925
+// libstdc++/40925 and LWG 811
void test01()
{
int *ip = 0;
@@ -52,10 +52,12 @@ void test01()
std::pair<int X::*, int X::*> p7(0, mp);
std::pair<int X::*, int X::*> p8(mp, mp);
- std::pair<int*, move_only> p9(0, move_only());
- std::pair<int X::*, move_only> p10(0, move_only());
- std::pair<move_only, int*> p11(move_only(), 0);
- std::pair<move_only, int X::*> p12(move_only(), 0);
+ // LWG 811 resolution doesn't support move-only types,
+ // so we have to use nullptr here not a literal 0.
+ std::pair<int*, move_only> p9(nullptr, move_only());
+ std::pair<int X::*, move_only> p10(nullptr, move_only());
+ std::pair<move_only, int*> p11(move_only(), nullptr);
+ std::pair<move_only, int X::*> p12(move_only(), nullptr);
std::pair<int*, move_only> p13(ip, move_only());
std::pair<int X::*, move_only> p14(mp, move_only());
diff --git a/libstdc++-v3/testsuite/20_util/pair/cons/99957.cc b/libstdc++-v3/testsuite/20_util/pair/cons/99957.cc
new file mode 100644
index 00000000000..d75ff21da60
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/pair/cons/99957.cc
@@ -0,0 +1,28 @@
+// { dg-options "-Wdeprecated" }
+// { dg-do compile { target c++11 } }
+
+#include <utility>
+
+using std::pair;
+
+struct MoveOnly
+{
+ MoveOnly() = default;
+ MoveOnly(MoveOnly&&) {}
+};
+
+struct ExplicitMoveOnly
+{
+ ExplicitMoveOnly() = default;
+ ExplicitMoveOnly(ExplicitMoveOnly&&) {}
+ explicit ExplicitMoveOnly(MoveOnly&&) {}
+};
+
+// PR libstdc++/99957
+// check non-standard constructors are deprecated
+
+pair<int*, ExplicitMoveOnly> v14{0, MoveOnly{}}; // { dg-warning "deprecated" }
+pair<ExplicitMoveOnly, int*> v15{MoveOnly{}, 0}; // { dg-warning "deprecated" }
+
+pair<int*, MoveOnly> v16 = {0, MoveOnly{}}; // { dg-warning "deprecated" }
+pair<MoveOnly, int*> v17 = {MoveOnly{}, 0}; // { dg-warning "deprecated" }
diff --git a/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc b/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
index 3d75e6dbb91..508ca32ecb7 100644
--- a/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
+++ b/libstdc++-v3/testsuite/20_util/pair/cons/explicit_construct.cc
@@ -126,10 +126,10 @@ struct ExplicitMoveOnly
explicit ExplicitMoveOnly(MoveOnly&&) {}
};
-std::pair<int*, ExplicitMoveOnly> v14{0, MoveOnly{}};
-std::pair<ExplicitMoveOnly, int*> v15{MoveOnly{}, 0};
+std::pair<int*, ExplicitMoveOnly> v14{nullptr, MoveOnly{}};
+std::pair<ExplicitMoveOnly, int*> v15{MoveOnly{}, nullptr};
std::pair<int*, ExplicitMoveOnly> v16 =
- {0, MoveOnly{}}; // { dg-error "could not convert" }
+ {nullptr, MoveOnly{}}; // { dg-error "could not convert" }
std::pair<ExplicitMoveOnly, int*> v17 =
- {MoveOnly{}, 0}; // { dg-error "could not convert" }
+ {MoveOnly{}, nullptr}; // { dg-error "could not convert" }
More information about the Libstdc++-cvs
mailing list