From 2b22ef0132e041917b6d8a566b12e955fea163b7 Mon Sep 17 00:00:00 2001
From: Felix Morgner <felix.morgner@gmail.com>
Date: Thu, 8 Jun 2023 14:52:36 +0200
Subject: derivations: introduce nt::contains concept

---
 source/lib/include/newtype/derivation_clause.hpp |  3 +++
 source/lib/include/newtype/newtype.hpp           | 15 +++++----------
 2 files changed, 8 insertions(+), 10 deletions(-)

diff --git a/source/lib/include/newtype/derivation_clause.hpp b/source/lib/include/newtype/derivation_clause.hpp
index 6de70e1..c4aa051 100644
--- a/source/lib/include/newtype/derivation_clause.hpp
+++ b/source/lib/include/newtype/derivation_clause.hpp
@@ -65,6 +65,9 @@ namespace nt
     }
   };
 
+  template<typename DerivationClause, auto Feature>
+  concept contains = requires(DerivationClause clause) { requires clause(Feature); };
+
 }  // namespace nt
 
 #endif
\ No newline at end of file
diff --git a/source/lib/include/newtype/newtype.hpp b/source/lib/include/newtype/newtype.hpp
index 126c439..33863ac 100644
--- a/source/lib/include/newtype/newtype.hpp
+++ b/source/lib/include/newtype/newtype.hpp
@@ -259,16 +259,14 @@ namespace nt
     return lhs.decay() == rhs.decay();
   }
 
-  template<nt::concepts::equality_comparable BaseType, typename TagType, auto DerivationClause>
-    requires(DerivationClause(nt::EqBase))
+  template<nt::concepts::equality_comparable BaseType, typename TagType, nt::contains<nt::EqBase> auto DerivationClause>
   auto constexpr operator==(new_type<BaseType, TagType, DerivationClause> const & lhs,
                             BaseType const & rhs) noexcept(nt::concepts::nothrow_equality_comparable<BaseType>) -> bool
   {
     return lhs.decay() == rhs;
   }
 
-  template<nt::concepts::equality_comparable BaseType, typename TagType, auto DerivationClause>
-    requires(DerivationClause(nt::EqBase))
+  template<nt::concepts::equality_comparable BaseType, typename TagType, nt::contains<nt::EqBase> auto DerivationClause>
   auto constexpr
   operator==(BaseType const & lhs,
              new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(nt::concepts::nothrow_equality_comparable<BaseType>) -> bool
@@ -284,16 +282,14 @@ namespace nt
     return lhs.decay() != rhs.decay();
   }
 
-  template<nt::concepts::inequality_comparable BaseType, typename TagType, auto DerivationClause>
-    requires(DerivationClause(nt::EqBase))
+  template<nt::concepts::inequality_comparable BaseType, typename TagType, nt::contains<nt::EqBase> auto DerivationClause>
   auto constexpr operator!=(new_type<BaseType, TagType, DerivationClause> const & lhs,
                             BaseType const & rhs) noexcept(nt::concepts::nothrow_inequality_comparable<BaseType>) -> bool
   {
     return lhs.decay() != rhs;
   }
 
-  template<nt::concepts::inequality_comparable BaseType, typename TagType, auto DerivationClause>
-    requires(DerivationClause(nt::EqBase))
+  template<nt::concepts::inequality_comparable BaseType, typename TagType, nt::contains<nt::EqBase> auto DerivationClause>
   auto constexpr
   operator!=(BaseType const & lhs,
              new_type<BaseType, TagType, DerivationClause> const & rhs) noexcept(nt::concepts::nothrow_inequality_comparable<BaseType>) -> bool
@@ -533,8 +529,7 @@ namespace nt
 
 namespace std
 {
-  template<typename BaseType, typename TagType, auto DerivationClause>
-    requires(nt::concepts::hashable<BaseType> && DerivationClause(nt::Hash))
+  template<nt::concepts::hashable BaseType, typename TagType, nt::contains<nt::Hash> auto DerivationClause>
   struct hash<nt::new_type<BaseType, TagType, DerivationClause>>
   {
     auto constexpr operator()(nt::new_type<BaseType, TagType, DerivationClause> const & object) const
-- 
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