utils: add Result / Option types

Add some Rust-style Result/Option types, based on TartanLlama's
expected, optional classes.

There's std::optional of course, but we can't depend on C++17 yet.

lib/utils/mu-result.hh

@@ -0,0 +1,39 @@
+/*
+** Copyright (C) 2019-2020 Dirk-Jan C. Binnema <djcb@djcbsoftware.nl>
+**
+** This program is free software; you can redistribute it and/or modify it
+** under the terms of the GNU General Public License as published by the
+** Free Software Foundation; either version 3, or (at your option) any
+** later version.
+**
+** This program 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 General Public License for more details.
+**
+** You should have received a copy of the GNU General Public License
+** along with this program; if not, write to the Free Software Foundation,
+** Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+**
+*/
+
+
+#ifndef MU_RESULT_HH__
+#define MU_RESULT_HH__
+
+
+#include "expected.hpp"
+#include "utils/mu-error.hh"
+
+
+namespace Mu {
+/**
+ * A Result is _either_ some value of type T, _or_ an error.
+ *
+ */
+template <typename T> using Result = tl::expected<T, Error>;
+
+} // namespace Mu
+
+
+#endif /* MU_ERROR_HH__ */