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.
llvm-svn: 153855
Cr-Mirrored-From: sso://chromium.googlesource.com/_direct/external/github.com/llvm/llvm-project
Cr-Mirrored-Commit: 0527c6207af5de565bbd77e64f953bbc785cee8d
diff --git a/include/__tuple b/include/__tuple
index 3b2be1c..8216804 100644
--- a/include/__tuple
+++ b/include/__tuple
@@ -216,7 +216,7 @@
template <class _Tp0, class ..._Tp, class _Up0, class ..._Up>
struct __tuple_convertible_imp<true, __tuple_types<_Tp0, _Tp...>, __tuple_types<_Up0, _Up...> >
: public integral_constant<bool,
- is_constructible<_Up0, _Tp0>::value &&
+ is_convertible<_Tp0, _Up0>::value &&
__tuple_convertible_imp<true, __tuple_types<_Tp...>, __tuple_types<_Up...> >::value> {};
template <>
@@ -235,6 +235,33 @@
typename __make_tuple_types<_Tp>::type, typename __make_tuple_types<_Up>::type>
{};
+// __tuple_constructible
+
+template <bool, class _Tp, class _Up>
+struct __tuple_constructible_imp : public false_type {};
+
+template <class _Tp0, class ..._Tp, class _Up0, class ..._Up>
+struct __tuple_constructible_imp<true, __tuple_types<_Tp0, _Tp...>, __tuple_types<_Up0, _Up...> >
+ : public integral_constant<bool,
+ is_constructible<_Up0, _Tp0>::value &&
+ __tuple_constructible_imp<true, __tuple_types<_Tp...>, __tuple_types<_Up...> >::value> {};
+
+template <>
+struct __tuple_constructible_imp<true, __tuple_types<>, __tuple_types<> >
+ : public true_type {};
+
+template <class _Tp, class _Up, bool = __tuple_like<typename remove_reference<_Tp>::type>::value,
+ bool = __tuple_like<_Up>::value>
+struct __tuple_constructible
+ : public false_type {};
+
+template <class _Tp, class _Up>
+struct __tuple_constructible<_Tp, _Up, true, true>
+ : public __tuple_constructible_imp<tuple_size<typename remove_reference<_Tp>::type>::value ==
+ tuple_size<_Up>::value,
+ typename __make_tuple_types<_Tp>::type, typename __make_tuple_types<_Up>::type>
+{};
+
// __tuple_assignable
template <bool, class _Tp, class _Up>