Trait Aggregate 

pub trait Aggregate:
    Default
    + Send
    + Sync {
    type Event: EventData;

    // Required methods
    fn stream_category() -> &'static str;
    fn apply(&mut self, event: &Self::Event);
}

The domain model whose state is rebuilt by folding events.

Why Default? In event sourcing, an aggregate’s state is defined by its event history. Default::default() represents the state before any events have been applied — a logically empty aggregate. All real state arises through apply. If your aggregate has fields that look invalid in their default form (e.g. BankAccount { open: false, owner: "".into() }), that’s correct — those values are unreachable in practice because the first event (e.g. Opened) will set them. Mire constructs the empty aggregate, then replays events onto it.

If your apply implementation guards against operating on a default aggregate (e.g. early-returns when !self.open), the invariants hold even if someone accidentally calls a method on a Default::default() instance — the events that would unlock real behaviour simply haven’t been applied yet.

Required Associated Types

type Event: EventData

Required Methods

fn stream_category() -> &'static str

The category prefix for streams of this aggregate type. Streams are identified as format!("{category}-{id}"); the category is what ProjectionRunners subscribe to and what EventStore::read_category_after filters on.

fn apply(&mut self, event: &Self::Event)

Fold a single event into the aggregate’s state. Must be deterministic and side-effect-free — it runs every time the aggregate is reloaded.

Dyn Compatibility

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety".

Implementors