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I believe tuple is still under development in the standard. Daniel Krugler is/will be making convincing arguments that a modified form of LWG 2051 (currently NAD Future) is easily acheivable and desirable. He has demonstrated that a tuple<T...> where all of the T are implicitly convertible from U... should have a tuple constructor that is also implicit, instead of explicit. This would support the use cases in LWG 2051 while not undermining T... with explicit conversions from U.... This check-in is an experimental implementation of Daniel's work. I believe this work to be mature enough to warrant inclusion into libc++. If anyone sees real-world problems that this check in causes, please let me know and I will revert it, and provide the feedback to the LWG.

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git-svn-id: https://llvm.org/svn/llvm-project/libcxx/trunk@153855 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Howard Hinnant
2012-04-01 23:10:42 +00:00
parent 9aa4e11451
commit dc1345fd44
4 changed files with 105 additions and 11 deletions
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58
include/tuple
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@@ -552,7 +552,7 @@ public:
) {}
template <class ..._Up,
class = typename enable_if
typename enable_if
<
sizeof...(_Up) <= sizeof...(_Tp) &&
__tuple_convertible
@@ -562,8 +562,40 @@ public:
sizeof...(_Up) < sizeof...(_Tp) ?
sizeof...(_Up) :
sizeof...(_Tp)>::type
>::value
>::type
>::value,
bool
>::type = false
>
_LIBCPP_INLINE_VISIBILITY
tuple(_Up&&... __u)
: base_(typename __make_tuple_indices<sizeof...(_Up)>::type(),
typename __make_tuple_types<tuple, sizeof...(_Up)>::type(),
typename __make_tuple_indices<sizeof...(_Tp), sizeof...(_Up)>::type(),
typename __make_tuple_types<tuple, sizeof...(_Tp), sizeof...(_Up)>::type(),
_VSTD::forward<_Up>(__u)...) {}
template <class ..._Up,
typename enable_if
<
sizeof...(_Up) <= sizeof...(_Tp) &&
__tuple_constructible
<
tuple<_Up...>,
typename __make_tuple_types<tuple,
sizeof...(_Up) < sizeof...(_Tp) ?
sizeof...(_Up) :
sizeof...(_Tp)>::type
>::value &&
!__tuple_convertible
<
tuple<_Up...>,
typename __make_tuple_types<tuple,
sizeof...(_Up) < sizeof...(_Tp) ?
sizeof...(_Up) :
sizeof...(_Tp)>::type
>::value,
bool
>::type =false
>
_LIBCPP_INLINE_VISIBILITY
explicit
@@ -598,15 +630,29 @@ public:
_VSTD::forward<_Up>(__u)...) {}
template <class _Tuple,
class = typename enable_if
typename enable_if
<
__tuple_convertible<_Tuple, tuple>::value
>::type
__tuple_convertible<_Tuple, tuple>::value,
bool
>::type = false
>
_LIBCPP_INLINE_VISIBILITY
tuple(_Tuple&& __t)
: base_(_VSTD::forward<_Tuple>(__t)) {}
template <class _Tuple,
typename enable_if
<
__tuple_constructible<_Tuple, tuple>::value &&
!__tuple_convertible<_Tuple, tuple>::value,
bool
>::type = false
>
_LIBCPP_INLINE_VISIBILITY
explicit
tuple(_Tuple&& __t)
: base_(_VSTD::forward<_Tuple>(__t)) {}
template <class _Alloc, class _Tuple,
class = typename enable_if
<