utils: Improve option/result types

And add the beginnings of unit tests.

lib/utils/test-option.cc

@@ -0,0 +1,59 @@
+/*
+** Copyright (C) 2020 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+**  This library is free software; you can 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.
+**
+**  This library is distributed in the hope that it will be useful,
+**  but WITHOUT ANY WARRANTY; without even the implied warranty of
+**  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+**  Lesser General Public License for more details.
+**
+**  You should have received a copy of the GNU Lesser General Public
+**  License along with this library; if not, write to the Free
+**  Software Foundation, 51 Franklin Street, Fifth Floor, Boston, MA
+**  02110-1301, USA.
+*/
+
+#include "mu-utils.hh"
+#include "mu-option.hh"
+
+using namespace Mu;
+
+static Option<int>
+get_opt_int (bool b)
+{
+        if (b)
+                return Some(123);
+        else
+                return Nothing;
+}
+
+static void
+test_option()
+{
+        {
+                const auto oi{get_opt_int(true)};
+                g_assert_true(!!oi);
+                g_assert_cmpint(oi.value(),==,123);
+        }
+
+        {
+                const auto oi{get_opt_int(false)};
+                g_assert_false(!!oi);
+                g_assert_false(oi.has_value());
+                g_assert_cmpint(oi.value_or(456),==,456);
+        }
+}
+
+int
+main (int argc, char *argv[])
+{
+	g_test_init (&argc, &argv, NULL);
+
+	g_test_add_func ("/option/option",  test_option);
+
+	return g_test_run ();
+}