Comment by haileys
The way to do this in idiomatic Rust is to make a wrapper type that implements drop:
struct MyForeignPtr(*mut c_void);
impl Drop for MyForeignPtr {
fn drop(&mut self) {
unsafe { my_free_func(self.0); }
}
}
In this case they seem to have Rust on both sides of the FFI API and seemingly want to avoid heap allocating the Vec's static parts, which makes sense.
So, an extended version if your solution would be to initialize the static parts on the stack using `MaybeUninit`, and `assume_init` on that after the call to get an `OwningArrayC<T>` out, which then can have a Drop impl defined for it.