Event registry¶

The event registry maps event type names to factory functions. Persistent event stores use it to deserialize events from storage.

Functions¶

RegisterEvent¶

func RegisterEvent[T any, PT eventPtr[T]](_ PT)

Registers an event type using its EventType() name as the key. The pointer passed in is only used to infer the concrete type T; the value itself is discarded. Each subsequent lookup gets a genuinely new new(T) instance — built at the type level via generics, not via reflection — so decoding two stored events never lets one overwrite the other's fields.

eventsourcing.RegisterEvent(&events.TaskCreated{})

RegisterEventByType¶

var RegisterEventByType func(fn func() Event)

Registers using a factory function. Equivalent to RegisterEvent but with explicit factory control:

eventsourcing.RegisterEventByType(func() eventsourcing.Event {
    return &events.TaskCreated{}
})

RegisterEventByName¶

var RegisterEventByName func(name string, fn func() Event)

Registers under a custom name, independent of EventType(). Useful for migration when stored event names differ from current type names.

// stored as "task.created" historically
eventsourcing.RegisterEventByName("task.created", func() eventsourcing.Event {
    return &events.TaskCreated{}
})

A single Go type can be registered under multiple names.

NewEventByName¶

var NewEventByName func(name string) (Event, error)

Creates a new instance of a registered event by name. Returns ErrEventNotRegistered if not found.

ev, err := eventsourcing.NewEventByName("TaskCreated")
if err != nil {
    // handle ErrEventNotRegistered
}
created := ev.(*events.TaskCreated)

EventNamesFor¶

var EventNamesFor func(event Event) []string

Returns all names under which the given event type is registered.

names := eventsourcing.EventNamesFor(&events.TaskCreated{})
// ["TaskCreated"] or ["TaskCreated", "task.created"] if registered under both

Used internally by EventGroupProcessor.StreamFilter().

Behaviour notes¶

RegisterEventByType, RegisterEventByName, NewEventByName, and EventNamesFor are package-level variables and can be replaced in tests to inject alternative implementations. RegisterEvent is a generic function and cannot be replaced this way — swap RegisterEventByType instead if you need to intercept registration.
Registration panics on nil factory, nil result, empty name, or duplicate name.
The registry is protected by a sync.RWMutex and is safe for concurrent reads.
Register all events at startup (typically in init() functions or main()).