Include test for identity

dune/common/test/CMakeLists.txt

@@ -306,6 +306,9 @@ dune_add_test(SOURCES singletontest.cc
 dune_add_test(SOURCES sllisttest.cc
               LABELS quick)
 
+dune_add_test(SOURCES stdidentity.cc
+              LABELS quick)
+
 dune_add_test(SOURCES stdapplytest.cc
               LINK_LIBRARIES dunecommon
               LABELS quick)

dune/common/test/stdidentity.cc

+// -*- tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+// vi: set et ts=4 sw=2 sts=2:
+
+#ifdef HAVE_CONFIG_H
+#include "config.h"
+#endif
+#include <dune/common/std/functional.hh>
+#include <iostream>
+#include <cassert>
+
+struct Foo {
+  static int count;
+  Foo() { ++count; std::cout << "construct" << std::endl; }
+  Foo(const Foo&) { ++count; std::cout << "copy construct" << std::endl; }
+  Foo(Foo&&) { ++count; std::cout << "move construct" << std::endl; }
+  ~Foo() { --count; std::cout << "deconstruct" << std::endl; }
+};
+int Foo::count = 0;
+
+template<typename T>
+T&& assert_count(T&& arg, int count)
+{
+  std::cout << std::decay_t<T>::count << std::endl;
+  assert(std::decay_t<T>::count == count);
+  return std::forward<T>(arg);
+}
+
+int main()
+{
+  auto id = Dune::Std::identity();
+
+  assert_count(id(Foo()),1); // pass an r-value to identity, still constructed on the assert
+
+  const auto& foo0 = id(Foo()); // pass an r-value to identity
+  assert_count(foo0,0); // id(Foo()) is alredy doconstructed at this point
+
+  auto foo1 = id(Foo()); // pass an r-value to identity and move it to foo1
+  assert_count(foo1,1); // foo0 is alredy doconstructed at this point
+
+  Foo foo2;
+  assert_count(id(foo2),2); // pass an l-value to identity
+
+  const auto& foo3 = id(foo2); // pass an l-value to identity
+  assert_count(foo3,2); // foo still exist at this point
+
+  auto foo4 = id(foo2); // pass an l-value to identity and copy its result
+  assert_count(foo4,3); // copy of foo still exist at this point
+}