From abd892af3a6f46e30681e93eadf449c68b399296 Mon Sep 17 00:00:00 2001 From: Eric Fiselier Date: Sun, 26 Jun 2016 21:01:34 +0000 Subject: [PATCH] Implement LWG 2488 - Make the placeholders constexpr. This patch makes the bind placeholders in std::placeholders both (1) const and (2) constexpr (See below). This is technically a breaking change for any code using the placeholders outside of std::bind and depending on them being non-const. However I don't think this will break any real world code. (1) Previously the placeholders were non-const extern globals in all dialects. This patch changes these extern globals to be const in all dialects. Since the cv-qualifiers don't participate in name mangling for globals this is an ABI compatible change. (2) Make the placeholders constexpr in C++11 and beyond. Although LWG 2488 only applies to C++17 I don't see any reason not to backport this change. git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@273824 91177308-0d34-0410-b5e6-96231b3b80d8 --- include/functional | 33 +++++++++++++------ src/bind.cpp | 21 ++++++------ .../func.bind.place/placeholders.pass.cpp | 28 ++++++++++++++++ www/cxx1z_status.html | 2 +- 4 files changed, 63 insertions(+), 21 deletions(-) diff --git a/include/functional b/include/functional index 9e4d5db41..a13772f31 100644 --- a/include/functional +++ b/include/functional @@ -1980,16 +1980,29 @@ namespace placeholders template struct __ph {}; -_LIBCPP_FUNC_VIS extern __ph<1> _1; -_LIBCPP_FUNC_VIS extern __ph<2> _2; -_LIBCPP_FUNC_VIS extern __ph<3> _3; -_LIBCPP_FUNC_VIS extern __ph<4> _4; -_LIBCPP_FUNC_VIS extern __ph<5> _5; -_LIBCPP_FUNC_VIS extern __ph<6> _6; -_LIBCPP_FUNC_VIS extern __ph<7> _7; -_LIBCPP_FUNC_VIS extern __ph<8> _8; -_LIBCPP_FUNC_VIS extern __ph<9> _9; -_LIBCPP_FUNC_VIS extern __ph<10> _10; +#if defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_BIND) +_LIBCPP_FUNC_VIS extern const __ph<1> _1; +_LIBCPP_FUNC_VIS extern const __ph<2> _2; +_LIBCPP_FUNC_VIS extern const __ph<3> _3; +_LIBCPP_FUNC_VIS extern const __ph<4> _4; +_LIBCPP_FUNC_VIS extern const __ph<5> _5; +_LIBCPP_FUNC_VIS extern const __ph<6> _6; +_LIBCPP_FUNC_VIS extern const __ph<7> _7; +_LIBCPP_FUNC_VIS extern const __ph<8> _8; +_LIBCPP_FUNC_VIS extern const __ph<9> _9; +_LIBCPP_FUNC_VIS extern const __ph<10> _10; +#else +constexpr __ph<1> _1{}; +constexpr __ph<2> _2{}; +constexpr __ph<3> _3{}; +constexpr __ph<4> _4{}; +constexpr __ph<5> _5{}; +constexpr __ph<6> _6{}; +constexpr __ph<7> _7{}; +constexpr __ph<8> _8{}; +constexpr __ph<9> _9{}; +constexpr __ph<10> _10{}; +#endif // defined(_LIBCPP_CXX03_LANG) || defined(_LIBCPP_BUILDING_BIND) } // placeholders diff --git a/src/bind.cpp b/src/bind.cpp index cab0b7c03..b318fc169 100644 --- a/src/bind.cpp +++ b/src/bind.cpp @@ -7,6 +7,7 @@ // //===----------------------------------------------------------------------===// +#define _LIBCPP_BUILDING_BIND #include "functional" _LIBCPP_BEGIN_NAMESPACE_STD @@ -14,16 +15,16 @@ _LIBCPP_BEGIN_NAMESPACE_STD namespace placeholders { -__ph<1> _1; -__ph<2> _2; -__ph<3> _3; -__ph<4> _4; -__ph<5> _5; -__ph<6> _6; -__ph<7> _7; -__ph<8> _8; -__ph<9> _9; -__ph<10> _10; +const __ph<1> _1{}; +const __ph<2> _2{}; +const __ph<3> _3{}; +const __ph<4> _4{}; +const __ph<5> _5{}; +const __ph<6> _6{}; +const __ph<7> _7{}; +const __ph<8> _8{}; +const __ph<9> _9{}; +const __ph<10> _10{}; } // placeholders diff --git a/test/std/utilities/function.objects/bind/func.bind/func.bind.place/placeholders.pass.cpp b/test/std/utilities/function.objects/bind/func.bind/func.bind.place/placeholders.pass.cpp index 246186040..68986ac1a 100644 --- a/test/std/utilities/function.objects/bind/func.bind/func.bind.place/placeholders.pass.cpp +++ b/test/std/utilities/function.objects/bind/func.bind/func.bind.place/placeholders.pass.cpp @@ -10,10 +10,14 @@ // // placeholders +// The placeholders are constexpr in C++17 and beyond. +// libc++ provides constexpr placeholders in C++11 and beyond. #include #include +#include "test_macros.h" + template void test(const T& t) @@ -28,6 +32,30 @@ test(const T& t) static_assert(std::is_nothrow_move_constructible::value, ""); } +#if TEST_STD_VER >= 11 +constexpr decltype(std::placeholders::_1) default1{}; +constexpr decltype(std::placeholders::_2) default2{}; +constexpr decltype(std::placeholders::_3) default3{}; +constexpr decltype(std::placeholders::_4) default4{}; +constexpr decltype(std::placeholders::_5) default5{}; +constexpr decltype(std::placeholders::_6) default6{}; +constexpr decltype(std::placeholders::_7) default7{}; +constexpr decltype(std::placeholders::_8) default8{}; +constexpr decltype(std::placeholders::_9) default9{}; +constexpr decltype(std::placeholders::_10) default10{}; + +constexpr decltype(std::placeholders::_1) cp1 = std::placeholders::_1; +constexpr decltype(std::placeholders::_2) cp2 = std::placeholders::_2; +constexpr decltype(std::placeholders::_3) cp3 = std::placeholders::_3; +constexpr decltype(std::placeholders::_4) cp4 = std::placeholders::_4; +constexpr decltype(std::placeholders::_5) cp5 = std::placeholders::_5; +constexpr decltype(std::placeholders::_6) cp6 = std::placeholders::_6; +constexpr decltype(std::placeholders::_7) cp7 = std::placeholders::_7; +constexpr decltype(std::placeholders::_8) cp8 = std::placeholders::_8; +constexpr decltype(std::placeholders::_9) cp9 = std::placeholders::_9; +constexpr decltype(std::placeholders::_10) cp10 = std::placeholders::_10; +#endif // TEST_STD_VER >= 11 + int main() { test(std::placeholders::_1); diff --git a/www/cxx1z_status.html b/www/cxx1z_status.html index fb25cf35f..e11b74265 100644 --- a/www/cxx1z_status.html +++ b/www/cxx1z_status.html @@ -161,7 +161,7 @@ 2467is_always_equal has slightly inconsistent defaultLenexaComplete 2470Allocator's destroy function should be allowed to fail to instantiateLenexaComplete 2482[c.strings] Table 73 mentions nonexistent functionsLenexaComplete - 2488Placeholders should be allowed and encouraged to be constexprLenexa + 2488Placeholders should be allowed and encouraged to be constexprLenexaComplete 1169num_get not fully compatible with strto*KonaComplete 2072Unclear wording about capacity of temporary buffersKonaComplete