add fake container-like datastructure with all no-op

src/amdis/common/CMakeLists.txt

@@ -10,6 +10,7 @@ install(FILES
     Concepts.hpp
     ConceptsBase.hpp
     ConcurrentCache.hpp
+    FakeContainer.hpp
     FieldMatVec.hpp
     FieldMatVec.inc.hpp
     Filesystem.hpp

src/amdis/common/FakeContainer.hpp

+#pragma once
+
+#include <cstddef>
+
+namespace AMDiS
+{
+  struct FakeAssigner
+  {
+    template <class T>
+    FakeAssigner& operator=(T&&) { return *this; }
+
+    template <class T>
+    FakeAssigner& operator+=(T&&) { return *this; }
+
+    template <class T>
+    FakeAssigner& operator-=(T&&) { return *this; }
+
+    template <class T>
+    FakeAssigner& operator*=(T&&) { return *this; }
+
+    template <class T>
+    FakeAssigner& operator/=(T&&) { return *this; }
+  };
+
+  /// A container-like data-structure not storing anything and with empty
+  /// implementations in many container-interface functions.
+  /**
+   * This container that *does nothing* can be used as a dummy argument to
+   * functions expecting a container, in order to ommit specializations of
+   * these functions for not providing a container.
+   **/
+  class FakeContainer
+      : public FakeAssigner
+  {
+  public:
+    using size_type = std::size_t;
+
+    template <class... Args>
+    FakeContainer(Args&&...) {}
+
+    template <class Arg>
+    void push_back(Arg&&) {}
+
+    template <class... Args>
+    void emplace_back(Args&&...) {}
+
+    void reserve(size_type) {}
+    void resize(size_type) {}
+
+    /// This container is always empty
+    bool empty() const { return true; }
+    size_type size() const { return 0u; }
+
+    /// Mutable *element* access does return the container itself
+    /// This allows to emulate nested containers
+    FakeContainer& operator[](size_type) { return *this; }
+
+    /// Assignment operators from a fake assigner
+    using FakeAssigner::operator=;
+    using FakeAssigner::operator+=;
+    using FakeAssigner::operator-=;
+    using FakeAssigner::operator*=;
+    using FakeAssigner::operator/=;
+
+    FakeAssigner front() { return {}; }
+    FakeAssigner back() { return {}; }
+
+    friend inline FakeAssigner front(FakeContainer&) { return {}; }
+    friend inline FakeAssigner back(FakeContainer&) { return {}; }
+  };
+
+} // end namespace AMDiS