v/vlib/eventbus/README.md

Event Bus

A module to provide eventing capabilities using pub/sub.

API

1. new() - create a new EventBus

Structs:

EventBus:

1. publish(name string, sender voidptr, args voidptr) - publish an event with provided Params & name
2. clear_all() - clear all subscribers
3. has_subscriber(name string) - check if a subscriber to an event exists

Subscriber:

1. subscribe(name string, handler EventHandlerFn) - subscribe to an event
2. subscribe_once(name string, handler EventHandlerFn) - subscribe only once to an event
3. subscribe_method(name string, handler EventHandlerFn, receiver voidptr) - subscribe to an event and also set the receiver as a parameter. Since it's not yet possible to send methods as parameters, this is a workaround.
4. is_subscribed(name string) - check if we are subscribed to an event
5. unsubscribe(name string) - unsubscribe from an event

Event Handler Signature:

The function given to subscribe, subscribe_method and subscribe_once must match this:

fn cb(receiver voidptr, args voidptr, sender voidptr) {
}

// Since V can map structs to voidptr, this also works
struct ClickEvent {
	x int
	y int
}

// Example case where publisher sends ClickEvent as args.
fn on_press(receiver voidptr, e &ClickEvent, sender voidptr) {
	println(e.x)
	// your code here...
}

Usage

For usage across modules check the example.

Note: As a general rule, you will need to subscribe before publishing.

main.v

module main

import eventbus

// initialize it globally
const (
	eb = eventbus.new()
)

fn main() {
	// get a mutable reference to the subscriber
	mut sub := eb.subscriber
	// subscribe to the 'error' event
	sub.subscribe('error', on_error)
	// start the work
	do_work()
}

// the event handler
fn on_error(receiver voidptr, e &Error, work &Work) {
	println('error occured on ${work.hours}. Error: $e.message')
}

work.v

module main

import eventbus

const eb = eventbus.new()

struct Work {
	hours int
}

struct AnError {
	message string
}

fn do_work() {
	work := Work{20}
	// get a mutable Params instance & put some data into it
	error := &AnError{'Error: no internet connection.'}
	// publish the event
	eb.publish('error', work, error)
}

Notes:

1. Each EventBus instance has it's own registry (i.e. there is no global event registry so you can't just subscribe to an event wherever you are.
2. Each EventBus has a Subscriber instance which will need to be either exposed or you can make small public helper functions specific to your module like (onPress, onError) and etc.
3. The eventbus module has some helpers to ease getting/setting of Params (since V doesn't support empty interfaces yet or reflection) so use them (see usage above).

The rationale behind separating Subscriber & Publisher:

This is mainly for security because if publisher & subscriber are both passed around, a client can easily publish events acting as the server. So a client should only be able to use the Subscriber methods.