Tests: add a test for Threads::InitializationCheck

tests/base/lazy_01.cc

@@ -0,0 +1,66 @@
+// ---------------------------------------------------------------------
+//
+// Copyright (C) 2005 - 2021 by the deal.II authors
+//
+// This file is part of the deal.II library.
+//
+// The deal.II library is free software; you can use it, redistribute
+// it, and/or modify it under the terms of the GNU Lesser General
+// Public License as published by the Free Software Foundation; either
+// version 2.1 of the License, or (at your option) any later version.
+// The full text of the license can be found in the file LICENSE.md at
+// the top level directory of deal.II.
+//
+// ---------------------------------------------------------------------
+
+
+#include <deal.II/base/lazy.h>
+
+#include <iostream>
+
+#include "../tests.h"
+
+using namespace dealii;
+
+int
+main()
+{
+  initlog();
+
+  {
+    Lazy<int> lazy_integer;
+
+    deallog << "lazy_integer.has_value() = " << lazy_integer.has_value()
+            << std::endl;
+
+    lazy_integer.initialize([&]() {
+      deallog << "[initializing object]" << std::endl;
+      return 42;
+    });
+    deallog << "lazy_integer.has_value() = " << lazy_integer.has_value() << "\n"
+            << "lazy_integer.value() = " << lazy_integer.value() << std::endl;
+
+    lazy_integer.initialize([&]() {
+      deallog << "[initializing object] again... not good." << std::endl;
+      return -1;
+    });
+
+    deallog << "lazy_integer.has_value() = " << lazy_integer.has_value() << "\n"
+            << "lazy_integer.value() = " << lazy_integer.value() << std::endl;
+  }
+
+  {
+    Lazy<int> lazy_integer;
+
+    deallog << "lazy_integer.value() = "
+            << lazy_integer.value_or_initialize([&]() {
+                 deallog << "... [initializing object] ... ";
+                 return 42;
+               })
+            << std::endl;
+  }
+
+
+  deallog << "OK!" << std::endl;
+  return 0;
+}

tests/base/lazy_01.output

@@ -0,0 +1,9 @@
+
+DEAL::lazy_integer.has_value() = 0
+DEAL::[initializing object]
+DEAL::lazy_integer.has_value() = 1
+lazy_integer.value() = 42
+DEAL::lazy_integer.has_value() = 1
+lazy_integer.value() = 42
+DEAL::lazy_integer.value() = ... [initializing object] ... 42
+DEAL::OK!