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Merge pull request #320 from boostorg/issue_305

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Add helper macro BOOST_IF_CONSTEXPR.
This commit is contained in:
jzmaddock
2020-02-24 12:16:04 +00:00
committed by GitHub
parent 79e92d9222 b54214277f
commit cc915f1055
3 changed files with 20 additions and 0 deletions
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1
doc/macro_reference.qbk
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@ -978,6 +978,7 @@ provide compliant C++17 support.
[table
[[Macro ][ Description ]]
[[`BOOST_INLINE_VARIABLE`][This macro expands to `inline` on compilers that support C++17 inline variables and to nothing otherwise. Users may need to check for `BOOST_NO_CXX17_INLINE_VARIABLES` for further adjustments to the code.]]
[[`BOOST_IF_CONSTEXPR`][Expands to `if constexpr` when supported, or `if` otherwise.]]
[[`BOOST_INLINE_CONSTEXPR`][This is a shortcut for `BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST`.]]
]

8
include/boost/config/detail/suffix.hpp
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@ -1002,6 +1002,14 @@ namespace std{ using ::type_info; }
#else
#define BOOST_INLINE_VARIABLE
#endif
//
// C++17 if constexpr
//
#if !defined(BOOST_NO_CXX17_IF_CONSTEXPR)
# define BOOST_IF_CONSTEXPR if constexpr
#else
# define BOOST_IF_CONSTEXPR if
#endif
#define BOOST_INLINE_CONSTEXPR BOOST_INLINE_VARIABLE BOOST_CONSTEXPR_OR_CONST

11
test/helper_macro_test.cpp
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@ -51,6 +51,12 @@ struct no_unique
BOOST_ATTRIBUTE_NO_UNIQUE_ADDRESS empty b;
};
template <bool b>
struct trait
{
enum { value = b };
};
int main()
{
@ -66,6 +72,11 @@ int main()
always_throw();
nodiscard_struct s;
no_unique no_un;
BOOST_IF_CONSTEXPR(trait<true>::value)
{
result += 2;
}
}
catch(int)
{