What are finalizers in Go (`runtime.SetFinalizer`)?

Finalizers attach a function to an object that the Garbage Collector calls before sweeping the object from memory.

They are akin to destructors in C++/C#. They are primarily used in Go for cleaning up CGO resources (C pointers) that the Go GC doesn't know how to free. They are highly unpredictable; the GC makes no guarantees about exactly when (or even if) a finalizer will run before the program exits.