Hi
I was trying to play with tuple implementation and was annoyed by
repetition of _Head type when instantiating _Head_base so I thought
about this patch.
How do you like it ?
I still need to run tests, will do before commit, ok ?
François
Index: include/std/tuple
===================================================================
--- include/std/tuple (revision 237045)
+++ include/std/tuple (working copy)
@@ -48,7 +48,24 @@
* @{
*/
- template<std::size_t _Idx, typename _Head, bool _IsEmptyNotFinal>
+ template<typename... _Elements>
+ class tuple;
+
+ template<typename _Tp>
+ struct __is_empty_non_tuple : is_empty<_Tp> { };
+
+ // Using EBO for elements that are tuples causes ambiguous base errors.
+ template<typename _El0, typename... _El>
+ struct __is_empty_non_tuple<tuple<_El0, _El...>> : false_type { };
+
+ // Use the Empty Base-class Optimization for empty, non-final types.
+ template<typename _Tp>
+ using __empty_not_final
+ = typename conditional<__is_final(_Tp), false_type,
+ __is_empty_non_tuple<_Tp>>::type;
+
+ template<std::size_t _Idx, typename _Head,
+ bool = __empty_not_final<_Head>::value>
struct _Head_base;
template<std::size_t _Idx, typename _Head>
@@ -158,19 +175,6 @@
template<std::size_t _Idx, typename... _Elements>
struct _Tuple_impl;
- template<typename _Tp>
- struct __is_empty_non_tuple : is_empty<_Tp> { };
-
- // Using EBO for elements that are tuples causes ambiguous base errors.
- template<typename _El0, typename... _El>
- struct __is_empty_non_tuple<tuple<_El0, _El...>> : false_type { };
-
- // Use the Empty Base-class Optimization for empty, non-final types.
- template<typename _Tp>
- using __empty_not_final
- = typename conditional<__is_final(_Tp), false_type,
- __is_empty_non_tuple<_Tp>>::type;
-
/**
* Recursive tuple implementation. Here we store the @c Head element
* and derive from a @c Tuple_impl containing the remaining elements
@@ -179,12 +183,12 @@
template<std::size_t _Idx, typename _Head, typename... _Tail>
struct _Tuple_impl<_Idx, _Head, _Tail...>
: public _Tuple_impl<_Idx + 1, _Tail...>,
- private _Head_base<_Idx, _Head, __empty_not_final<_Head>::value>
+ private _Head_base<_Idx, _Head>
{
template<std::size_t, typename...> friend class _Tuple_impl;
typedef _Tuple_impl<_Idx + 1, _Tail...> _Inherited;
- typedef _Head_base<_Idx, _Head, __empty_not_final<_Head>::value> _Base;
+ typedef _Head_base<_Idx, _Head> _Base;
static constexpr _Head&
_M_head(_Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
@@ -336,11 +340,11 @@
// Basis case of inheritance recursion.
template<std::size_t _Idx, typename _Head>
struct _Tuple_impl<_Idx, _Head>
- : private _Head_base<_Idx, _Head, __empty_not_final<_Head>::value>
+ : private _Head_base<_Idx, _Head>
{
template<std::size_t, typename...> friend class _Tuple_impl;
- typedef _Head_base<_Idx, _Head, __empty_not_final<_Head>::value> _Base;
+ typedef _Head_base<_Idx, _Head> _Base;
static constexpr _Head&
_M_head(_Tuple_impl& __t) noexcept { return _Base::_M_head(__t); }
@@ -457,9 +461,6 @@
}
};
- template<typename... _Elements>
- class tuple;
-
// Concept utility functions, reused in conditionally-explicit
// constructors.
template<bool, typename... _Elements>
