utils: add auto_raii helper function

this helper permits to register a resource and cleanup function to keep
exception safety with C like resource. For exemple, to be sure that a
FILE* will be closed, you can use:

auto file = auto_raii(fopen("filename"), fclose);

file will auto cast to FILE* when needed, and will call fclose when
going out of scope.

src/utils.hh

@@ -39,6 +39,35 @@ bool operator== (const std::unique_ptr<T>& lhs, T* rhs)
     return lhs.get() == rhs;
 }
 
+template<typename T, typename F>
+class AutoRaii
+{
+public:
+    AutoRaii(T* resource, F cleanup)
+        : m_resource(resource), m_cleanup(cleanup) {}
+
+    AutoRaii(AutoRaii&& other) : m_resource(other.m_resource),
+                                 m_cleanup(other.m_cleanup)
+    { other.m_resource = nullptr; }
+
+    AutoRaii(const AutoRaii&) = delete;
+    AutoRaii& operator=(const AutoRaii&) = delete;
+
+    ~AutoRaii() { if (m_resource) m_cleanup(m_resource); }
+
+    operator T*() { return m_resource; }
+
+private:
+    T* m_resource;
+    F  m_cleanup;
+};
+
+template<typename T, typename F>
+AutoRaii<T, F> auto_raii(T* resource, F cleanup)
+{
+    return AutoRaii<T, F>(resource, cleanup);
+}
+
 }
 
 #endif // utils_hh_INCLUDED