From 943033bc921bb328bbc354f15627dbf4bd6ab1e4 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Sat, 22 Feb 2020 18:29:07 +0100
Subject: new_type: fix enablement of begin

---
 include/newtype/impl/type_traits_extensions.hpp | 23 +---------------
 include/newtype/new_type.hpp                    | 25 +++++++++++++-----
 test/src/iterable_suite.cpp                     | 35 +++++++++++++++++++++----
 3 files changed, 49 insertions(+), 34 deletions(-)

diff --git a/include/newtype/impl/type_traits_extensions.hpp b/include/newtype/impl/type_traits_extensions.hpp
index 7096578..80ba5b0 100644
--- a/include/newtype/impl/type_traits_extensions.hpp
+++ b/include/newtype/impl/type_traits_extensions.hpp
@@ -6,7 +6,6 @@
 #include <cstddef>
 #include <functional>
 #include <iosfwd>
-#include <iterator>
 #include <type_traits>
 
 namespace nt::impl
@@ -1054,26 +1053,6 @@ namespace nt::impl
 
   inline namespace iterable
   {
-    template<typename T, typename = void>
-    struct has_std_begin : std::false_type
-    {
-    };
-
-    template<typename T>
-    struct has_std_begin<T, std::void_t<decltype(std::begin(std::declval<T &>()))>>
-        : std::is_same<typename T::iterator, std::remove_cvref_t<decltype(std::begin(std::declval<T &>()))>>
-    {
-    };
-
-    template<typename T>
-    struct has_std_begin<T const, std::void_t<decltype(std::begin(std::declval<T const &>()))>>
-        : std::is_same<typename T::const_iterator, std::remove_cvref_t<decltype(std::begin(std::declval<T const &>()))>>
-    {
-    };
-
-    template<typename T>
-    auto constexpr has_std_begin_v = has_std_begin<T>::value;
-
     template<typename T, typename = void>
     struct has_free_begin : std::false_type
     {
@@ -1115,7 +1094,7 @@ namespace nt::impl
     auto constexpr has_member_begin_v = has_member_begin<T>::value;
 
     template<typename T>
-    struct has_begin : std::disjunction<has_std_begin<T>, has_free_begin<T>, has_member_begin<T>>
+    struct has_begin : std::disjunction<has_free_begin<T>, has_member_begin<T>>
     {
     };
 
diff --git a/include/newtype/new_type.hpp b/include/newtype/new_type.hpp
index 0cf6ec3..0db01b2 100644
--- a/include/newtype/new_type.hpp
+++ b/include/newtype/new_type.hpp
@@ -10,7 +10,6 @@
 
 #include <functional>
 #include <istream>
-#include <iterator>
 #include <ostream>
 #include <type_traits>
 
@@ -62,6 +61,16 @@ namespace nt
         -> std::enable_if_t<DerivationClauseV(nt::Arithmetic) && impl::is_divide_assignable_v<BaseTypeT>,
                             new_type<BaseTypeT, TagTypeT, DerivationClauseV> &>;
 
+    template<typename BaseTypeT, typename TagTypeT, auto DerivationClauseV>
+    auto constexpr friend begin(new_type<BaseTypeT, TagTypeT, DerivationClauseV> & obj)
+        -> std::enable_if_t<DerivationClauseV(nt::Iterable) && impl::has_free_begin_v<BaseTypeT>,
+                            typename new_type<BaseTypeT, TagTypeT, DerivationClauseV>::iterator>;
+
+    template<typename BaseTypeT, typename TagTypeT, auto DerivationClauseV>
+    auto constexpr friend begin(new_type<BaseTypeT, TagTypeT, DerivationClauseV> const & obj)
+        -> std::enable_if_t<DerivationClauseV(nt::Iterable) && impl::has_free_begin_v<BaseTypeT>,
+                            typename new_type<BaseTypeT, TagTypeT, DerivationClauseV>::const_iterator>;
+
     using super = impl::new_type_move_assignment<BaseType, TagType>;
 
   public:
@@ -448,21 +457,23 @@ namespace nt
   /**
    * Get an iterator to the beginning of the object contained by an instance of new_type
    */
-  template<typename BaseType, typename TagType, auto DerivationClause, typename NewType = new_type<BaseType, TagType, DerivationClause>>
+  template<typename BaseType, typename TagType, auto DerivationClause>
   auto constexpr begin(new_type<BaseType, TagType, DerivationClause> & obj)
-      -> std::enable_if_t<DerivationClause(nt::Iterable) && impl::has_free_begin_v<BaseType>, typename NewType::iterator>
+      -> std::enable_if_t<DerivationClause(nt::Iterable) && impl::has_free_begin_v<BaseType>,
+                          typename new_type<BaseType, TagType, DerivationClause>::iterator>
   {
-    return begin(obj);
+    return begin(obj.m_value);
   }
 
   /**
    * Get a constant iterator to the beginning of the object contained by an instance of new_type
    */
-  template<typename BaseType, typename TagType, auto DerivationClause, typename NewType = new_type<BaseType, TagType, DerivationClause>>
+  template<typename BaseType, typename TagType, auto DerivationClause>
   auto constexpr begin(new_type<BaseType, TagType, DerivationClause> const & obj)
-      -> std::enable_if_t<DerivationClause(nt::Iterable) && impl::has_free_begin_v<BaseType const>, typename NewType::const_iterator>
+      -> std::enable_if_t<DerivationClause(nt::Iterable) && impl::has_free_begin_v<BaseType const>,
+                          typename new_type<BaseType, TagType, DerivationClause>::const_iterator>
   {
-    return begin(obj);
+    return begin(obj.m_value);
   }
 
 }  // namespace nt
diff --git a/test/src/iterable_suite.cpp b/test/src/iterable_suite.cpp
index 2470571..bf478e1 100644
--- a/test/src/iterable_suite.cpp
+++ b/test/src/iterable_suite.cpp
@@ -14,7 +14,16 @@
 namespace
 {
 
-}
+  struct with_member
+  {
+    using iterator = void *;
+    using const_iterator = void const *;
+
+    auto begin() -> iterator;
+    auto begin() const -> const_iterator;
+  };
+
+}  // namespace
 
 inline namespace begin_tests
 {
@@ -34,18 +43,32 @@ inline namespace begin_tests
 
   auto a_new__type_based_on_an_iterable_type_with_member_begin_deriving_iterable_has_member_begin() -> void
   {
-    static_assert(nt::impl::has_member_begin_v<std::array<int, 3>>);
-    using type_alias = nt::new_type<std::array<int, 3>, struct tag, deriving(nt::Iterable)>;
+    static_assert(nt::impl::has_member_begin_v<with_member>);
+    using type_alias = nt::new_type<with_member, struct tag, deriving(nt::Iterable)>;
     ASSERT(nt::impl::has_member_begin_v<type_alias>);
   }
 
   auto a_new__type_based_on_an_iterable_type_with_constant_member_begin_deriving_iterable_has_constant_member_begin() -> void
   {
-    static_assert(nt::impl::has_member_begin_v<std::array<int const, 3>>);
-    using type_alias = nt::new_type<std::array<int, 3>, struct tag, deriving(nt::Iterable)>;
+    static_assert(nt::impl::has_member_begin_v<with_member const>);
+    using type_alias = nt::new_type<with_member, struct tag, deriving(nt::Iterable)>;
     ASSERT(nt::impl::has_member_begin_v<type_alias const>);
   }
 
+  auto a_new__type_based_on_an_iterable_type_without_free_begin_deriving_iterable_has_no_free_begin() -> void
+  {
+    static_assert(!nt::impl::has_free_begin_v<with_member>);
+    using type_alias = nt::new_type<with_member, struct tag, deriving(nt::Iterable)>;
+    ASSERT(!nt::impl::has_free_begin_v<type_alias>);
+  }
+
+  auto a_new__type_based_on_an_iterable_type_without_constant_free_begin_deriving_iterable_has_no_constant_free_begin() -> void
+  {
+    static_assert(!nt::impl::has_free_begin_v<with_member const>);
+    using type_alias = nt::new_type<with_member, struct tag, deriving(nt::Iterable)>;
+    ASSERT(!nt::impl::has_free_begin_v<type_alias const>);
+  }
+
 }  // namespace begin_tests
 
 auto iterable_suite() -> std::pair<cute::suite, std::string>
@@ -56,6 +79,8 @@ auto iterable_suite() -> std::pair<cute::suite, std::string>
               KAWAII(a_new__type_based_on_a_non_iterable_type_deriving_iterable_has_no_begin),
               KAWAII(a_new__type_based_on_an_iterable_type_with_member_begin_deriving_iterable_has_member_begin),
               KAWAII(a_new__type_based_on_an_iterable_type_with_constant_member_begin_deriving_iterable_has_constant_member_begin),
+              KAWAII(a_new__type_based_on_an_iterable_type_without_free_begin_deriving_iterable_has_no_free_begin),
+              KAWAII(a_new__type_based_on_an_iterable_type_without_constant_free_begin_deriving_iterable_has_no_constant_free_begin),
           },
           "Iterable Tests"};
 }
\ No newline at end of file
-- 
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