From 51e0bed20ad915401898306d409ff29b7e8015ad Mon Sep 17 00:00:00 2001
From: Eidolon <furyhunter600@gmail.com>
Date: Mon, 12 Dec 2022 16:40:56 -0600
Subject: [PATCH] c++: add finally RAII utility

This mirrors the `finally` utility in Guidelines Support Library for
ensuring that a cleanup function is always called when the utility
object leaves scope, even when unwinding the stack from an exception.
This is to aid in transitioning malloc/free pairs in function bodies to
be more exception-safe.
---
 src/cxxutil.hpp | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)
 create mode 100644 src/cxxutil.hpp

diff --git a/src/cxxutil.hpp b/src/cxxutil.hpp
new file mode 100644
index 000000000..befe9c20b
--- /dev/null
+++ b/src/cxxutil.hpp
@@ -0,0 +1,37 @@
+#ifndef __SRB2_CXXUTIL_HPP__
+#define __SRB2_CXXUTIL_HPP__
+
+#include <type_traits>
+#include <utility>
+
+namespace srb2 {
+
+template <class F>
+class Finally {
+public:
+	explicit Finally(const F& f) noexcept : f_(f) {}
+	explicit Finally(F&& f) noexcept : f_(f) {}
+
+	Finally(Finally&& from) noexcept : f_(std::move(from.f_)), call_(std::exchange(from.call_, false)) {}
+
+	Finally(const Finally& from) = delete;
+	void operator=(const Finally& from) = delete;
+	void operator=(Finally&& from) = delete;
+
+	~Finally() noexcept {
+		f_();
+	}
+
+private:
+	F f_;
+	bool call_ = true;
+};
+
+template <class F>
+Finally<std::decay_t<F>> finally(F&& f) noexcept {
+	return Finally {std::forward<F>(f)};
+}
+
+}
+
+#endif // __SRB2_CXXUTIL_HPP__