ircd::util: Add scope_count tool.

include/ircd/util/scope_count.h

@@ -0,0 +1,45 @@
+// 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_SCOPE_COUNT_H
+
+namespace ircd::util
+{
+	struct scope_count;
+};
+
+/// A simple boiler-plate for incrementing a counter when constructed and
+/// decrementing it to its previous value when destructed. This takes a runtime
+/// reference to that counter.
+struct ircd::util::scope_count
+{
+	ulong *count {nullptr};
+
+	scope_count(ulong &count);
+	scope_count(const scope_count &) = delete;
+	scope_count(scope_count &&) noexcept = delete;
+	~scope_count() noexcept;
+};
+
+inline
+ircd::util::scope_count::scope_count(ulong &count)
+:count{&count}
+{
+	++count;
+}
+
+inline
+ircd::util::scope_count::~scope_count()
+noexcept
+{
+	assert(count);
+	--(*count);
+}

include/ircd/util/util.h

@@ -46,6 +46,7 @@ namespace ircd
 #include "tuple.h"
 #include "timer.h"
 #include "scope_light.h"
+#include "scope_count.h"
 #include "life_guard.h"
 #include "pubsetbuf.h"
 #include "string.h"