Provide a concept specification of a field types

dune/common/concepts/field.hh

@@ -5,18 +5,6 @@
 #ifndef DUNE_COMMON_CONCEPTS_FIELD_HH
 #define DUNE_COMMON_CONCEPTS_FIELD_HH
 
-// check whether c++20 concept can be used
-#if __has_include(<version>) && __has_include(<concepts>)
-  #include <version>
-  #if  __cpp_concepts >= 201907L && __cpp_lib_concepts >= 202002L
-    #ifndef DUNE_ENABLE_CONCEPTS
-    #define DUNE_ENABLE_CONCEPTS 1
-    #endif
-  #endif
-#endif
-
-#if DUNE_ENABLE_CONCEPTS
-
 #include <concepts>
 #include <limits>
 
@@ -61,6 +49,4 @@ static_assert(Field<Dune::Concept::Archetypes::Field>);
 
 } // end namespace Dune::Concept
 
-#endif // DUNE_ENABLE_CONCEPTS
-
 #endif // DUNE_COMMON_CONCEPTS_FIELD_HH

dune/common/concepts/identity.hh

@@ -11,11 +11,11 @@
 
 namespace Dune::Concept {
 
-//! Zero is the neutral element of the addition
+//! Identity is the neutral element of type `T` of the operation `Op`
 template <class T, class Op>
 struct Identity;
 
-// Primary template depends on specializations of the template Zero
+// Primary template depends on specializations of the template Identity
 template <class T, class Op>
 constexpr auto identity (T value, Op) noexcept
   -> decltype(Identity<T,Op>{}(value))

dune/common/concepts/inverse.hh

@@ -12,11 +12,11 @@
 
 namespace Dune::Concept {
 
-//! Zero is the neutral element of the addition
+//! Inverse is the inverse element of type `T` of the operation `Op`
 template <class T, class Op>
 struct Inverse;
 
-// Primary template depends on specializations of the template Zero
+// Primary template depends on specializations of the template Inverse
 template <class T, class Op>
 constexpr auto inverse (T value, Op) noexcept
   -> decltype(Inverse<T,Op>{}(value))