From 235dde40ee7e54cac63eea643fffee308b09595a Mon Sep 17 00:00:00 2001
From: Baptiste Wicht <baptiste.wicht@gmail.com>
Date: Sat, 3 Sep 2016 20:06:35 +0200
Subject: [PATCH] Completely review std::tuple

---
 tstl/include/integer_sequence.hpp |  71 ++++++++
 tstl/include/nth_type.hpp         |  30 ++++
 tstl/include/tuple.hpp            | 286 +++++++++++++++++++++---------
 3 files changed, 303 insertions(+), 84 deletions(-)
 create mode 100644 tstl/include/integer_sequence.hpp
 create mode 100644 tstl/include/nth_type.hpp

diff --git a/tstl/include/integer_sequence.hpp b/tstl/include/integer_sequence.hpp
new file mode 100644
index 00000000..ddfd4b10
--- /dev/null
+++ b/tstl/include/integer_sequence.hpp
@@ -0,0 +1,71 @@
+//=======================================================================
+// Copyright Baptiste Wicht 2013-2016.
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+
+#ifndef TSTL_INTEGER_SEQUENCE_H
+#define TSTL_INTEGER_SEQUENCE_H
+
+#include<types.hpp>
+#include<enable_if.hpp>
+
+namespace std {
+
+template<typename T, T... Values>
+struct integer_sequence {
+    static constexpr size_t size() noexcept {
+        return sizeof...(Values);
+    }
+};
+
+template <size_t... Values>
+using index_sequence = integer_sequence<size_t, Values...>;
+
+template <typename, size_t, bool>
+struct sequence_concat_impl;
+
+template <typename T, T... I, size_t N>
+struct sequence_concat_impl<integer_sequence<T, I...>, N, false> {
+    using type = integer_sequence<T, I..., (N + I)...>;
+};
+
+template <typename T, T... I, size_t N>
+struct sequence_concat_impl<integer_sequence<T, I...>, N, true> {
+    using type = integer_sequence<T, I..., (N + I)..., 2 * N>;
+};
+
+// The 0 and 1 cannot be deduced directly, must use SFINAE
+
+// Base type for generating a sequence
+template <typename T, T N, typename Enable = void>
+struct make_integer_sequence_impl;
+
+// The general case construct a list by concatenating
+template <typename T, T N, typename Enable>
+struct make_integer_sequence_impl {
+    using type = typename sequence_concat_impl<typename make_integer_sequence_impl<T, N / 2>::type, N / 2, N % 2 == 1>::type;
+};
+
+// Specialization for empty sequence
+template <typename T, T N>
+struct make_integer_sequence_impl<T, N, std::enable_if_t<(N == 0)>> {
+    using type = integer_sequence<T>;
+};
+
+// Specialization for sequence of length one
+template <typename T, T N>
+struct make_integer_sequence_impl<T, N, std::enable_if_t<(N == 1)>> {
+    using type = integer_sequence<T, 0>;
+};
+
+template <typename T, T N>
+using make_integer_sequence = typename make_integer_sequence_impl<T, N>::type;
+
+template <size_t N>
+using make_index_sequence = make_integer_sequence<size_t, N>;
+
+} //end of namespace std
+
+#endif
diff --git a/tstl/include/nth_type.hpp b/tstl/include/nth_type.hpp
new file mode 100644
index 00000000..b823e8dd
--- /dev/null
+++ b/tstl/include/nth_type.hpp
@@ -0,0 +1,30 @@
+//=======================================================================
+// Copyright Baptiste Wicht 2013-2016.
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE_1_0.txt or copy at
+//  http://www.boost.org/LICENSE_1_0.txt)
+//=======================================================================
+
+#ifndef TSTL_NTH_TYPE_H
+#define TSTL_NTH_TYPE_H
+
+#include<types.hpp>
+
+namespace std {
+
+template<size_t I, size_t S, typename Head, typename... Tail>
+struct nth_type_impl {
+    using type = typename nth_type_impl<I+1, S, Tail...>::type;
+};
+
+template<size_t I, typename Head, typename... Tail>
+struct nth_type_impl<I, I, Head, Tail...> {
+    using type = Head;
+};
+
+template<size_t I, typename... Tail>
+using nth_type_t = typename nth_type_impl<0, I, Tail...>::type;
+
+} //end of namespace std
+
+#endif
diff --git a/tstl/include/tuple.hpp b/tstl/include/tuple.hpp
index 3b1492c7..32f76cb2 100644
--- a/tstl/include/tuple.hpp
+++ b/tstl/include/tuple.hpp
@@ -9,105 +9,223 @@
 #define TUPLE_H
 
 #include<types.hpp>
+#include<enable_if.hpp>
+#include<utility.hpp> // std::forward / std::move
+#include<integer_sequence.hpp>
+#include<nth_type.hpp>
 
 namespace std {
 
-/*
- Base class used to store the head of the tuple impl. If
- the head type is an empty type, use EBO to optimize size
-*/
+template <typename... T>
+struct tuple;
 
-template<size_t I, typename H, bool Empty>
-struct head_base;
-
-template<size_t I, typename H>
-struct head_base<I, H, true> : H {
-    head_base() : H(){}
-    head_base(const H& h) : H(h){}
-
-    static H& head(head_base& b){ return b; }
-    static const H& head(const head_base& b){ return b; }
-};
-
-template<size_t I, typename H>
-struct head_base<I, H, false> {
-    H head_impl;
-
-    head_base() : head_impl(){}
-    head_base(const H& h) : head_impl(h){}
-
-    static H& head(head_base& b){ return b.head_impl; }
-    static const H& head(const head_base& b){ return b.head_impl; }
-};
-
-/* Tuple implementation */
-
-template<size_t I, typename... E>
-struct tuple_impl;
-
-template<size_t I>
-struct tuple_impl<I> {};
-
-template<size_t I, typename H, typename... E>
-struct tuple_impl<I, H, E...> : public tuple_impl<I + 1, E...>, private head_base<I, H, __is_empty(H)> {
-    typedef tuple_impl<I + 1, E...> parent_t;
-    typedef head_base<I, H, __is_empty(H)> base_parent_t;
-
-    tuple_impl() : parent_t(), base_parent_t() {}
-
-    explicit tuple_impl(const H& head, const E&... elements): parent_t(elements...), base_parent_t(head) {}
-
-    static H& head(tuple_impl& t){ return base_parent_t::head(t); }
-    static const H& head(const tuple_impl& t){ return base_parent_t::head(t); }
-};
-
-/* tuple class */
-
-template<typename... E>
-struct tuple : tuple_impl<0, E...> {
-    typedef tuple_impl<0, E...> parent_t;
-
-    tuple() : parent_t(){}
-
-    explicit tuple(const E&... elements): parent_t(elements...) {}
-};
-
-/* Helper to get the type of a tuple */
-
-template<size_t I, typename T>
+template <size_t I, typename T>
 struct tuple_element;
 
-template<size_t I, typename H, typename... T>
-struct tuple_element<I, tuple<H, T...>> : tuple_element<I - 1, tuple<T...>> { };
-
-template<typename H, typename... T>
-struct tuple_element<0, tuple<H, T...>> {
-    typedef H type;
+template <size_t I, typename... T>
+struct tuple_element<I, tuple<T...>> {
+    using type = nth_type_t<I, T...>;
 };
 
-template<int I, typename H, typename... T>
-inline H& get_helper(tuple_impl<I, H, T...>& t){
-    return tuple_impl<I, H, T...>::head(t);
+template <size_t I, typename... T>
+using tuple_element_t = typename tuple_element<I, T...>::type;
+
+template <size_t I, typename... T>
+const tuple_element_t<I, T...>& get(const tuple<T...>& v) noexcept;
+
+template <size_t I, typename... T>
+tuple_element_t<I, T...>& get(tuple<T...>& v) noexcept ;
+
+template <size_t I, typename... T>
+tuple_element_t<I, T...>&& get(tuple<T...>&& v) noexcept ;
+
+template<size_t I, typename T, typename Enable = void>
+struct tuple_value {
+    T value;
+
+    constexpr tuple_value(){}
+
+    tuple_value(const T& value) : value(value) {
+        //Nothing else to init
+    }
+
+    template <typename U>
+    tuple_value(U&& value) : value(std::forward<U>(value)) {
+        //Nothing else to init
+    }
+
+    tuple_value( const tuple_value& ) = default;
+    tuple_value( tuple_value&& ) = default;
+
+    template <typename U>
+    tuple_value& operator=(U&& value){
+        this->value = std::forward<U>(value);
+
+        return *this;
+    }
+
+    T& get() noexcept {
+        return value;
+    }
+
+    const T& get() const noexcept {
+        return value;
+    }
+};
+
+template<size_t I, typename T>
+struct tuple_value<I, T, std::enable_if_t<__is_empty(T)>> : private T {
+    constexpr tuple_value(){}
+
+    tuple_value(const T& value) : T(value) {
+        //Nothing else to init
+    }
+
+    template <typename U>
+    tuple_value(U&& value) : T(std::forward<U>(value)) {
+        //Nothing else to init
+    }
+
+    tuple_value( const tuple_value& ) = default;
+    tuple_value( tuple_value&& ) = default;
+
+    template <typename U>
+    tuple_value& operator=(U&& value){
+        static_cast<T&>(*this) = std::forward<U>(value);
+
+        return *this;
+    }
+
+    T& get() noexcept {
+        return static_cast<T&>(*this);
+    }
+
+    const T& get() const noexcept {
+        return static_cast<const T&>(*this);
+    }
+};
+
+using swallow = bool[];
+
+template <typename, typename...>
+struct tuple_base;
+
+template <size_t... I, typename... T>
+struct tuple_base<std::index_sequence<I...>, T...> : tuple_value<I, T>... {
+    constexpr tuple_base() = default;
+
+    template<typename... U, typename = std::enable_if_t<(sizeof...(U) == sizeof...(T))>>
+    constexpr explicit tuple_base(U&&... values) : tuple_value<I, T>(std::forward<U>(values))... {
+        //Nothing else to init
+    }
+
+    template <typename... U>
+    constexpr explicit tuple_base(const tuple<U...>& values) : tuple_value<I, T>(get<I>(values))... {
+        //Nothing else to init
+    }
+
+    template <typename... U>
+    constexpr explicit tuple_base(tuple<U...>&& values) : tuple_value<I, T>(std::forward<U>(get<I>(values)))... {
+        //Nothing else to init
+    }
+
+    tuple_base( const tuple_base& ) = default;
+    tuple_base( tuple_base&& ) = default;
+
+    tuple_base& operator=(const tuple_base& v) {
+        (void)swallow{(tuple_value<I, T>::operator=(static_cast<tuple_value<I, T>&>(v).get()), true)...};
+        return *this;
+    }
+
+    tuple_base& operator=(tuple_base&& v) {
+        (void)swallow{(tuple_value<I, T>::operator=(std::forward<T>(static_cast<tuple_value<I, T>&>(v).get())), true)...};
+        return *this;
+    }
+
+    template <typename... U>
+    tuple_base& operator=(const tuple<U...>& v) {
+        (void)swallow{(tuple_value<I, T>::operator=(get<I>(v)), true)...};
+        return *this;
+    }
+
+    template <typename... U>
+    tuple_base& operator=(tuple<U...>&& v) {
+        (void)swallow{(tuple_value<I, T>::operator=(get<I>(std::move(v))), true)...};
+        return *this;
+    }
+};
+
+template <typename... T>
+struct tuple {
+    using base_t = tuple_base<std::make_index_sequence<sizeof...(T)>, T...>;
+
+    base_t base;
+
+    constexpr tuple() : base(){
+        //Nothing else to init
+    }
+
+    constexpr tuple(const T&... values) : base(values...) {
+        //Nothing else to init
+    }
+
+    template<typename... U, typename = std::enable_if_t<(sizeof...(U) == sizeof...(T))>>
+    constexpr tuple(U&&... values) : base(std::forward<U>(values)...) {
+        //Nothing else to init
+    }
+
+    tuple( const tuple& ) = default;
+    tuple( tuple&& ) = default;
+
+    template<typename... U>
+    constexpr tuple(const tuple<U...>& v) : base(v) {
+        //Nothing else to init
+    }
+
+    template<typename... U>
+    constexpr tuple(tuple<U...>&& v) : base(std::move(v)) {
+        //Nothing else to init
+    }
+
+    template<typename TT>
+    tuple& operator=(TT&& value){
+        base = std::forward<TT>(value);
+
+        return *this;
+    }
+};
+
+template <typename T>
+struct tuple_size;
+
+template <typename... T>
+struct tuple_size<tuple<T...>> {
+    static constexpr const size_t value = sizeof...(T);
+};
+
+template <size_t I, typename... T>
+const nth_type_t<I, T...>& get(const tuple<T...>& v) noexcept {
+    return static_cast<const tuple_value<I, nth_type_t<I, T...>>&>(v.base).get();
 }
 
-template<int I, typename H, typename... T>
-inline const H& get_helper(const tuple_impl<I, H, T...>& t) {
-    return tuple_impl<I, H, T...>::head(t);
+template <size_t I, typename... T>
+nth_type_t<I, T...>& get(tuple<T...>& v) noexcept {
+    return static_cast<tuple_value<I, nth_type_t<I, T...>>&>(v.base).get();
 }
 
-template<int I, typename... E>
-inline typename tuple_element<I, tuple<E...> >::type& get(tuple<E...>& t){
-    return get_helper<I>(t);
-}
-
-template<int I, typename... E>
-inline const typename tuple_element<I, tuple<E...> >::type get(const tuple<E...>& t){
-    return get_helper<I>(t);
+template <size_t I, typename... T>
+nth_type_t<I, T...>&& get(tuple<T...>&& v) noexcept {
+    return static_cast<nth_type_t<I, T...>&&>(static_cast<tuple_value<I, nth_type_t<I, T...>>&&>(v.base).get());
 }
 
 template<typename... E>
-inline tuple<E...> make_tuple(E... args){
-    return tuple<E...>(args...);
+inline tuple<E...> make_tuple(E&&... args){
+    return tuple<E...>(std::forward<E>(args)...);
+}
+
+template< class... Types >
+constexpr tuple<Types&...> tie( Types&... args ){
+    return tuple<Types&...>(args...);
 }
 
 } //end of namespace std