Resolve concept loops with functions

This commit replaces the lambda in unevaluated contexts with an explicit function. This makes the code more portable as there is no need for a compiler that supports [temp.deduct/9], for example, Apple Clang 15. On the other hand it makes the code slightly less readable.

dune/grid/concepts.hh

@@ -13,10 +13,6 @@
  * In order to enable these concepts, you need the following:
  *  (i)   A C++20 compiler with concepts (i.e. __cpp_concepts >= 201907L)
  *  (ii)  The concepts in the standard library (i.e. __cpp_lib_concepts >= 202002L)
- *  (iii) A C++ compiler that supports unevaluated context lambdas (i.e.
- *        can compile `using = decltype([]{})`). This is automatically tested by
- *        CMake and exposed as a macro definition
- *        `DUNE_HAVE_CXX_UNEVALUATED_CONTEXT_LAMBDA`.
  *
  * - `gcc>=9` and `clang>=12` are known to fulfill (i) and (iii).
  * - `libstdc++>10` and `libc++>=13` are known to fulfill (ii).
@@ -25,7 +21,7 @@
 // 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 && DUNE_HAVE_CXX_UNEVALUATED_CONTEXT_LAMBDA
+  #if  __cpp_concepts >= 201907L && __cpp_lib_concepts >= 202002L
     #ifndef DUNE_GRID_HAVE_CONCEPTS
     #define DUNE_GRID_HAVE_CONCEPTS 1
     #endif

dune/grid/concepts/entity.hh

@@ -8,9 +8,9 @@
 #include <concepts>
 #include <utility>
 
+#include <dune/common/rangeutilities.hh>
 #include <dune/geometry/type.hh>
 #include <dune/grid/common/gridenums.hh>
-#include <dune/grid/concepts/entity.hh>
 #include <dune/grid/concepts/geometry.hh>
 #include <dune/grid/concepts/archetypes/entity.hh>
 
@@ -62,12 +62,9 @@ namespace Impl {
     { e.template subEntity<codim>(subEntity) } -> EntityGeneral;
   };
 
-  template<class E, int first, int last>
-  concept EntityAllCodimsExtended = requires(std::make_integer_sequence<int,last-first> codims)
-  {
-    []<int... c>(std::integer_sequence<int,c...>)
-        requires (EntityCodimExtended<E,(first+c)> &&...) {} (codims);
-  };
+  template<typename E, std::size_t... c>
+  void entityAllCodimsExtended(std::integer_sequence<std::size_t,c...>)
+   requires (EntityCodimExtended<E,int(c)> &&...);
 
 } // end namespace Impl
 
@@ -96,7 +93,9 @@ requires(const E e, int maxLevel)
   requires std::same_as<E, typename E::template Codim<0>::Entity>;
 } &&
 Impl::EntityCodimExtended<E,0> &&
-Impl::EntityAllCodimsExtended<E,1,E::dimension+1>;
+requires (index_constant<1> from, index_constant<E::dimension+1> to) {
+  Impl::entityAllCodimsExtended<E>(range(from, to).indices());
+};
 
 /**
  * @brief Model of a grid entity

dune/grid/concepts/grid.hh

@@ -66,12 +66,9 @@ namespace Impl {
       };
   } && GridCodimAllPartitions<G,codim>;
 
-  template<class G, int first, int last>
-  concept GridAllCodims = requires(std::make_integer_sequence<int,last-first> codims)
-  {
-    []<int... c>(std::integer_sequence<int,c...>)
-        requires (GridCodim<G,(first+c)> &&...) {} (codims);
-  };
+  template<class G, std::size_t... c>
+  void gridAllCodims(std::index_sequence<c...>)
+    requires (GridCodim<G,int(c)> &&...);
 
 } // end namespace Impl
 
@@ -149,7 +146,9 @@ requires(const G cg, int level, int codim, Dune::GeometryType type)
   };
 } &&
 Impl::GridCodim<G,0> &&
-Impl::GridAllCodims<G,1,G::dimension+1>;
+requires (index_constant<1> from, index_constant<G::dimension+1> to) {
+  Impl::gridAllCodims<G>(range(from, to).indices());
+};
 
 } // end namespace Dune::Concept
 

dune/grid/concepts/gridview.hh

@@ -64,12 +64,11 @@ namespace Impl {
     requires (not Dune::Capabilities::hasEntityIterator<Grid,codim>::v)
   void requireGridViewCodim() {}
 
-  template <class GV, int first, int last>
-  concept GridViewAllCodims = requires(std::make_integer_sequence<int,last-first> codims)
-  {
-    []<int... c>(std::integer_sequence<int,c...>) requires
-      requires { (requireGridViewCodim<GV,typename GV::Grid,(first+c)>(),...); } {} (codims);
-  };
+  template <class GV, std::size_t... c>
+  void gridViewAllCodims(std::index_sequence<c...>)
+    requires requires {
+      (requireGridViewCodim<GV,typename GV::Grid,int(c)>(),...);
+    };
 
 } // end namespace Impl
 
@@ -105,7 +104,9 @@ requires(const GV gv, int codim, Dune::GeometryType type)
   };
 } &&
 Impl::GridViewCodim<GV,0> &&
-Impl::GridViewAllCodims<GV,1,GV::dimension+1>;
+requires (index_constant<1> from, index_constant<GV::dimension+1> to) {
+  Impl::gridViewAllCodims<GV>(range(from, to).indices());
+};
 
 }  // end namespace Dune::Concept
 

dune/grid/concepts/indexidset.hh

@@ -28,12 +28,9 @@ namespace Impl {
     { is.contains(entity)                      } -> std::convertible_to<bool>;
   };
 
-  template<class IS, int first, int last>
-  concept IndexSetEntityAllCodims = requires(std::make_integer_sequence<int,last-first> codims)
-  {
-    []<int... c>(std::integer_sequence<int,c...>)
-        requires (IndexSetEntityCodim<IS,(first+c)> &&...) {} (codims);
-  };
+  template<class IS, std::size_t... c>
+  void indexSetEntityAllCodims(std::integer_sequence<std::size_t,c...>)
+    requires (IndexSetEntityCodim<IS,int(c)> &&...);
 
 } // end namespace Impl
 
@@ -56,8 +53,9 @@ concept IndexSet = requires(const IS is, Dune::GeometryType type, int codim)
   { is.size(codim)  } -> std::convertible_to<typename IS::IndexType>;
 } &&
 Impl::IndexSetEntityCodim<IS,0> &&
-Impl::IndexSetEntityAllCodims<IS,1,IS::dimension+1>;
-
+requires (index_constant<1> from, index_constant<IS::dimension+1> to) {
+  Impl::indexSetEntityAllCodims<IS>(range(from, to).indices());
+};
 
 namespace Impl {
 
@@ -69,12 +67,9 @@ namespace Impl {
     { is.id(entity)                 } -> std::same_as<typename IS::IdType>;
   };
 
-  template<class IS, int first, int last>
-  concept IdSetEntityAllCodims = requires(std::make_integer_sequence<int,last-first> codims)
-  {
-    []<int... c>(std::integer_sequence<int,c...>)
-        requires (IdSetEntityCodim<IS,(first+c)> &&...) {} (codims);
-  };
+  template<class IS, std::size_t... c>
+  void idSetEntityAllCodims(std::integer_sequence<std::size_t,c...>)
+    requires (IdSetEntityCodim<IS,int(c)> &&...);
 
 } // end namespace Impl
 
@@ -92,7 +87,9 @@ concept IdSet = requires(const IS is, const typename IS::template Codim<0>::Enti
   { is.subId(entity,i,cc) } -> std::same_as<typename IS::IdType>;
 } &&
 Impl::IdSetEntityCodim<IS,0> &&
-Impl::IdSetEntityAllCodims<IS,1,IS::dimension+1>;
+requires (index_constant<1> from, index_constant<IS::dimension+1> to) {
+  Impl::idSetEntityAllCodims<IS>(range(from, to).indices());
+};
 
 } // end namespace Dune::Concept