v/vlib/eventbus

Event Bus

A module to provide eventing capabilities using pub/sub.

API

1. new() - create a new EventBus

Structs:

EventBus:

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

Subscriber:

1. subscribe(string, fn(voidptr, Params)) - subscribe to an event
2. subscribe_once(string, fn(voidptr, Params)) - subscribe only once to an event
3. is_subscribed(string) - check if we are subscribed to an event
4. unsubscribe(string) - unsubscribe from an event

Event Handler Signature:

The function given to subscribe and subscribe_once must match this:

fn(voidptr, Params){

}
// Example
fn onPress(sender voidptr, p Params){
    //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(sender voidptr, p eventbus.Params) {
    //cast the sender to the real type
    //you can also make this mutable if required.
    work := *(*Work(sender)) //a little verbose but works

    error := p.get_string("error")
	println('error occured on ${work.hours}. Error: ${error}')
}

work.v

module main

import (
	eventbus
)

struct Work{
    hours int
}

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

How to use Params:

mut params := eventbus.Params{}

params.put_string("string", "some_string")
params.put_int("int", 20)
params.put_bool("bool", true)

// add maps and arrays of any type like this
arr := [1,2,3]
params.put_array("array", arr)
mp :=  {"hello": "world"}
params.put_map("map", mp)

//get and use the params like this
assert params.get_string("string") == "some_string"
assert params.get_int("int") == 20
assert params.get_bool("bool") == true

g_arr := params.get_array("array", 0)
assert g_arr[0] == 1

g_m := params.get_map("map", "")
assert g_m["hello"] == "world"

Caution when putting arrays:

Currently putting arrays and maps directly as parameters in put_array doesn't work, so make a variable first and use that.

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 the 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.