util: add scope_guard

This custom small implementation avoids adding an extra dependency like
Boost.ScopeExit

include/util/scope_guard.hpp

@@ -0,0 +1,21 @@
+#pragma once
+
+#include <utility>
+
+namespace waybar::util {
+
+template <typename Func>
+class scope_guard {
+ public:
+  explicit scope_guard(Func&& exit_function) : f{std::forward<Func>(exit_function)} {}
+  scope_guard(const scope_guard&) = delete;
+  scope_guard(scope_guard&&) = default;
+  scope_guard& operator=(const scope_guard&) = delete;
+  scope_guard& operator=(scope_guard&&) = default;
+  ~scope_guard() { f(); }
+
+ private:
+  Func f;
+};
+
+}  // namespace waybar::util