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Implement LWG 2488 - Make the placeholders constexpr.

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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
This commit is contained in:
Eric Fiselier
2016-06-26 21:01:34 +00:00
parent 5078baa9e0
commit abd892af3a
4 changed files with 63 additions and 21 deletions
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28
test/std/utilities/function.objects/bind/func.bind/func.bind.place/placeholders.pass.cpp
View File

@@ -10,10 +10,14 @@
// <functional>
// placeholders
// The placeholders are constexpr in C++17 and beyond.
// libc++ provides constexpr placeholders in C++11 and beyond.
#include <functional>
#include <type_traits>
#include "test_macros.h"
template <class T>
void
test(const T& t)
@@ -28,6 +32,30 @@ test(const T& t)
static_assert(std::is_nothrow_move_constructible<T>::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);