ircd::util: Add maybe() exception tool.

include/ircd/util/maybe.h

@@ -0,0 +1,77 @@
+// Matrix Construct
+//
+// Copyright (C) Matrix Construct Developers, Authors & Contributors
+// Copyright (C) 2016-2019 Jason Volk <jason@zemos.net>
+//
+// Permission to use, copy, modify, and/or distribute this software for any
+// purpose with or without fee is hereby granted, provided that the above
+// copyright notice and this permission notice is present in all copies. The
+// full license for this software is available in the LICENSE file.
+
+#pragma once
+#define HAVE_IRCD_UTIL_MAYBE_H
+
+namespace ircd { inline namespace util
+{
+	template<class function>
+	using maybe_retval = typename std::invoke_result<function>::type;
+
+	template<class function>
+	using maybe_type = std::tuple<maybe_retval<function>, std::exception_ptr>;
+
+	template<class function>
+	constexpr bool maybe_void();
+	using maybe_void_type = std::tuple<bool, std::exception_ptr>;
+
+	template<class function>
+	typename std::enable_if<!maybe_void<function>(), maybe_type<function>>::type
+	maybe(function &&) noexcept;
+
+	template<class function>
+	typename std::enable_if<maybe_void<function>(), maybe_void_type>::type
+	maybe(function &&) noexcept;
+}}
+
+template<class function>
+typename std::enable_if<!ircd::util::maybe_void<function>(), ircd::util::maybe_type<function>>::type
+ircd::util::maybe(function&& f)
+noexcept try
+{
+	return
+	{
+		f(), std::exception_ptr{}
+	};
+}
+catch(...)
+{
+	return
+	{
+		{}, std::current_exception()
+	};
+}
+
+template<class function>
+typename std::enable_if<ircd::util::maybe_void<function>(), ircd::util::maybe_void_type>::type
+ircd::util::maybe(function&& f)
+noexcept try
+{
+	f();
+	return
+	{
+		true, std::exception_ptr{}
+	};
+}
+catch(...)
+{
+	return
+	{
+		false, std::current_exception()
+	};
+}
+
+template<class function>
+constexpr bool
+ircd::util::maybe_void()
+{
+	return std::is_same<maybe_retval<function>, void>();
+}

include/ircd/util/util.h

@@ -63,6 +63,7 @@ namespace ircd
 #include "closure.h"
 #include "test.h"
 #include "boolean.h"
+#include "maybe.h"
 
 // Unsorted section
 namespace ircd {