new_type: fix enablement of begin

2 files changed, 19 insertions, 29 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
@@ -1055,26 +1054,6 @@ 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