Re: [PATCH V2 2/4] libgpiod: Add rust wrappers

[Bartosz Golaszewski <brgl@xxxxxxxx>]

On Fri, Dec 17, 2021 at 10:32 AM Viresh Kumar <viresh.kumar@xxxxxxxxxx> wrote:
>
> On 17-12-21, 10:12, Bartosz Golaszewski wrote:
> > No, it's a different story altogether. In C the buffer allocates
> > memory for events and when you "get" an event, you only have a pointer
> > to the memory space in the buffer that you must not free. But you can
> > "copy" an event with gpiod_edge_event_copy() which returns you a deep
> > copy of the event that will survive the parent and that must be freed
> > with gpiod_edge_event_free(). This is done so that by default we try
> > to limit the number of allocations (as there can be a lot of events)
> > unless the user decides to manually copy the event.
> >
> > In C++ I used that mechanism together with the buffer's const
> > event_get() and event's copy assignment operator. "Getting" an event
> > returns a const reference to the event (still in buffer's memory) but
> > copying it triggers a deep copy. The memory management is of course
> > handled by the destructor.
> >
> > This is not used in Python as speed is no longer a concern and we'd be
> > creating new python objects anyway. But in Rust, I think it makes
> > sense to reuse this mechanism.
>
> Ahh, what about this then, it just caches all the values when the event is
> requested ?
>
> pub struct EdgeEvent {
>     event_type: LineEdgeEvent,
>     timestamp: Duration,
>     line_offset: u32,
>     global_seqno: u64,
>     line_seqno: u64,
> }
>

Then does it make sense to make it a binding to libgpiod? :)

I don't know Rust that well to be able to come up with an idea off the
top of my head but I assume inheritance in one way or another exists
in rust? Can you have an EdgeEvent interface implemented by two
specialized structs, one that's stored in the buffer (stores a pointer
to the internal event) and one that stores the copy (and frees it when
it goes out of scope)?

Bart