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Rewrite std::get<Type>(...) helper using constexpr functions.

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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@274418 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eric Fiselier
2016-07-02 03:18:30 +00:00
parent 5fb1e0ab01
commit 22c3e76205
6 changed files with 62 additions and 119 deletions
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54
include/tuple
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@@ -986,39 +986,39 @@ get(const tuple<_Tp...>&& __t) _NOEXCEPT
}
#if _LIBCPP_STD_VER > 11
// get by type
template <typename _T1, size_t _Idx, typename... _Args>
struct __find_exactly_one_t_helper;
// -- find exactly one
template <typename _T1, size_t _Idx, typename... _Args>
struct __find_exactly_one_t_checker {
static constexpr size_t value = _Idx;
// Check the rest of the list to make sure there's only one
static_assert ( __find_exactly_one_t_helper<_T1, 0, _Args...>::value == -1, "type can only occur once in type list" );
};
namespace __find_detail {
static constexpr size_t __not_found = -1;
static constexpr size_t __ambiguous = __not_found - 1;
template <typename _T1, size_t _Idx>
struct __find_exactly_one_t_helper <_T1, _Idx> {
static constexpr size_t value = -1;
};
inline _LIBCPP_INLINE_VISIBILITY
constexpr size_t __find_idx_return(size_t __curr_i, size_t __res, bool __matches) {
return !__matches ? __res :
(__res == __not_found ? __curr_i : __ambiguous);
}
template <typename _T1, size_t _Idx, typename _Head, typename... _Args>
struct __find_exactly_one_t_helper <_T1, _Idx, _Head, _Args...> {
static constexpr size_t value =
std::conditional<
std::is_same<_T1, _Head>::value,
__find_exactly_one_t_checker<_T1, _Idx, _Args...>,
__find_exactly_one_t_helper <_T1, _Idx+1, _Args...>
>::type::value;
};
template <size_t _Nx>
inline _LIBCPP_INLINE_VISIBILITY
constexpr size_t __find_idx(size_t __i, const bool (&__matches)[_Nx]) {
return __i == _Nx ? __not_found :
__find_idx_return(__i, __find_idx(__i + 1, __matches), __matches[__i]);
}
template <class _T1, class ..._Args>
struct __find_exactly_one_checked {
static constexpr bool __matches[] = {is_same<_T1, _Args>::value...};
static constexpr size_t value = __find_detail::__find_idx(0, __matches);
static_assert (value != __not_found, "type not found in type list" );
static_assert(value != __ambiguous,"type occurs more than once in type list");
};
} // namespace __find_detail;
template <typename _T1, typename... _Args>
struct __find_exactly_one_t {
static constexpr size_t value = __find_exactly_one_t_helper<_T1, 0, _Args...>::value;
static_assert ( value != -1, "type not found in type list" );
};
struct __find_exactly_one_t
: public __find_detail::__find_exactly_one_checked<_T1, _Args...> {
};
template <class _T1, class... _Args>
inline _LIBCPP_INLINE_VISIBILITY