Update operations

So far we've implemented only insertion and retrieval operations.
Let's see how we can expand the system to provide an update operation.

Legacy updates

In the non-threaded version of the system, updates were fairly straightforward: TicketStore exposed a get_mut method that allowed the caller to obtain a mutable reference to a ticket, and then modify it.

Multithreaded updates

The same strategy won't work in the current multithreaded version. The borrow checker would stop us: SyncSender<&mut Ticket> isn't 'static because &mut Ticket doesn't satisfy the 'static lifetime, therefore they can't be captured by the closure that gets passed to std::thread::spawn.

There are a few ways to work around this limitation. We'll explore a few of them in the following exercises.

Patching

We can't send a &mut Ticket over a channel, therefore we can't mutate on the client-side.
Can we mutate on the server-side?

We can, if we tell the server what needs to be changed. In other words, if we send a patch to the server:

#![allow(unused)]
fn main() {
struct TicketPatch {
    id: TicketId,
    title: Option<TicketTitle>,
    description: Option<TicketDescription>,
    status: Option<TicketStatus>,
}
}

The id field is mandatory, since it's required to identify the ticket that needs to be updated.
All other fields are optional:

• If a field is None, it means that the field should not be changed.
• If a field is Some(value), it means that the field should be changed to value.

Exercise

The exercise for this section is located in 07_threads/10_patch