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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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21
src/bind.cpp
View File

@@ -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