From eb13bd9991ceef34cacb0913df90045b08726f81 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Thu, 8 Jun 2023 17:31:29 +0200
Subject: concepts: replace is_*_output_streamable*

---
 source/lib/include/newtype/concepts.hpp            | 15 ++++++++++
 .../newtype/impl/type_traits_extensions.hpp        | 33 ----------------------
 source/lib/include/newtype/newtype.hpp             | 10 ++++---
 source/tests/src/io_operators.cpp                  |  2 +-
 4 files changed, 22 insertions(+), 38 deletions(-)

diff --git a/source/lib/include/newtype/concepts.hpp b/source/lib/include/newtype/concepts.hpp
index c053612..c9ef951 100644
--- a/source/lib/include/newtype/concepts.hpp
+++ b/source/lib/include/newtype/concepts.hpp
@@ -54,6 +54,21 @@ namespace nt::concepts
     } noexcept;
   };
 
+  template<typename SubjectType, typename CharType, typename StreamTraits>
+  concept output_streamable = requires(SubjectType subject) {
+    {
+      std::declval<std::basic_ostream<CharType, StreamTraits> &>() << subject
+    } -> std::same_as<std::basic_ostream<CharType, StreamTraits> &>;
+  };
+
+  template<typename SubjectType, typename CharType, typename StreamTraits>
+  concept nothrow_output_streamable = requires(SubjectType subject) {
+    requires output_streamable<SubjectType, CharType, StreamTraits>;
+    {
+      std::declval<std::basic_ostream<CharType, StreamTraits> &>() << subject
+    } noexcept;
+  };
+
   template<typename SubjectType>
   concept hashable = requires(SubjectType subject) {
     {
diff --git a/source/lib/include/newtype/impl/type_traits_extensions.hpp b/source/lib/include/newtype/impl/type_traits_extensions.hpp
index 7db8e66..22834f2 100644
--- a/source/lib/include/newtype/impl/type_traits_extensions.hpp
+++ b/source/lib/include/newtype/impl/type_traits_extensions.hpp
@@ -124,39 +124,6 @@ namespace nt::impl
     auto constexpr is_nothrow_greater_than_equal_to_comparable_v = is_nothrow_greater_than_equal_to_comparable<T>::value;
   }  // namespace relationally_comparable
 
-  inline namespace iostreamable
-  {
-
-    template<typename StreamType, typename T, typename = void>
-    struct is_output_streamable : std::false_type
-    {
-    };
-
-    template<typename StreamType, typename T>
-    struct is_output_streamable<StreamType, T, std::void_t<decltype(std::declval<StreamType &>() << std::declval<T const &>())>>
-        : std::true_type
-    {
-    };
-
-    template<typename StreamType, typename T>
-    auto constexpr is_output_streamable_v = is_output_streamable<StreamType, T>::value;
-
-    template<typename StreamType, typename T, typename = void>
-    struct is_nothrow_output_streamable : std::false_type
-    {
-    };
-
-    template<typename StreamType, typename T>
-    struct is_nothrow_output_streamable<StreamType, T, std::void_t<decltype(std::declval<StreamType &>() << std::declval<T const &>())>>
-        : std::bool_constant<noexcept(std::declval<StreamType &>() << std::declval<T const &>())>
-    {
-    };
-
-    template<typename StreamType, typename T>
-    auto constexpr is_nothrow_output_streamable_v = is_nothrow_output_streamable<StreamType, T>::value;
-
-  }  // namespace iostreamable
-
   inline namespace arithmetic
   {
 
diff --git a/source/lib/include/newtype/newtype.hpp b/source/lib/include/newtype/newtype.hpp
index acfd2f9..e40097d 100644
--- a/source/lib/include/newtype/newtype.hpp
+++ b/source/lib/include/newtype/newtype.hpp
@@ -335,11 +335,13 @@ namespace nt
     return lhs.decay() >= rhs.decay();
   }
 
-  template<typename BaseType, typename TagType, auto DerivationClause, typename CharType, typename StreamTraits>
+  template<typename CharType,
+           typename StreamTraits,
+           nt::concepts::output_streamable<CharType, StreamTraits> BaseType,
+           typename TagType,
+           nt::contains<nt::Show> auto DerivationClause>
   auto operator<<(std::basic_ostream<CharType, StreamTraits> & output, new_type<BaseType, TagType, DerivationClause> const & source) noexcept(
-      impl::is_nothrow_output_streamable_v<std::basic_ostream<CharType, StreamTraits>, BaseType>)
-      -> std::enable_if_t<DerivationClause(nt::Show) && impl::is_output_streamable_v<std::basic_ostream<CharType, StreamTraits>, BaseType>,
-                          std::basic_ostream<CharType, StreamTraits>> &
+      nt::concepts::nothrow_output_streamable<BaseType, CharType, StreamTraits>) -> std::basic_ostream<CharType, StreamTraits> &
   {
     return output << source.decay();
   }
diff --git a/source/tests/src/io_operators.cpp b/source/tests/src/io_operators.cpp
index 23be171..2be41eb 100644
--- a/source/tests/src/io_operators.cpp
+++ b/source/tests/src/io_operators.cpp
@@ -83,7 +83,7 @@ SCENARIO("Stream Output")
     using type_alias = nt::new_type<int, struct tag, deriving(nt::Show)>;
     static_assert(has_stream_output_v<type_alias::base_type>);
 
-    THEN("it has the stream input operator")
+    THEN("it has the stream output operator")
     {
       STATIC_REQUIRE(has_stream_output_v<type_alias>);
     }
-- 
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