Variable

import { Variable } from "astal"

Variable is just a simple GObject that holds a value. And has shortcuts for hooking up subprocesses.

INFO

The Variable object imported from the "astal" package is not Astal.Variable.

Variable as state

const myvar = Variable<string>("initial-value")

// whenever its value changes, callback will be executed
myvar.subscribe((value: string) => {
    console.log(value)
})

// settings its value
myvar.set("new value")

// getting its value
const value = myvar.get()

// binding them to widgets
Widget.Label({
    label: bind(myvar).as((value) => `transformed ${value}`),
    label: myvar((value) => `transformed ${value}`), // shorthand for the above
})

WARNING

Make sure to make the transform functions pure. The .get() function can be called anytime by astal especially when deriving, so make sure there are no sideeffects.

Composing variables

Using Variable.derive we can compose both Variables and Bindings.

const v1: Variable<number> = Variable(2)
const v2: Variable<number> = Variable(3)

// first argument is a list of dependencies
// second argument is a transform function,
// where the parameters are the values of the dependencies in the order they were passed
const v3: Variable<number> = Variable.derive([v1, v2], (v1, v2) => {
    return v1 * v2
})

const b1: Binding<string> = bind(obj, "prop")
const b2: Binding<string> = bind(obj, "prop")

const b3: Variable<string> = Variable.derive([b1, b2], (b1, b2) => {
    return `${b1}-${b2}`
})

Subprocess shorthands

Using .poll and .watch we can start subprocess and capture their output in Variables. They can poll and watch at the same time, but they can only poll/watch one subprocess.

WARNING

The command parameter is passed to execAsync which means they are not executed in a shell environment, they do not expand env variables like $HOME, and they do not handle logical operators like && and ||.

If you want bash, run them with bash.

Variable("").poll(1000, ["bash", "-c", "command $VAR && command"])

const myVar = Variable<number>(0)
    .poll(1000, "command", (out: string, prev: number) => parseInt(out))
    .poll(1000, ["bash", "-c", "command"], (out, prev) => parseInt(out))
    .poll(1000, (prev) => prev + 1)

const myVar = Variable<number>(0)
    .watch("command", (out: string, prev: number) => parseInt(out))
    .watch(["bash", "-c", "command"], (out, prev) => parseInt(out))

You can temporarily stop them and restart them whenever.

myvar.stopWatch() // this kills the subprocess
myvar.stopPoll()

myvar.startListen() // launches the subprocess again
myvar.startPoll()

console.log(myvar.isListening())
console.log(myvar.isPolling())

Gobject connection shorthands

Using .observe you can connect gobject signals and capture their value.

const myvar = Variable("")
    .observe(obj1, "signal", () => "")
    .observe(obj2, "signal", () => "")

Dispose if no longer needed

This will stop the interval and force exit the subprocess and disconnect gobjects.

myVar.drop()

WARNING

Don't forget to drop them when they are defined inside widgets with either .poll, .watch or .observe

function MyWidget() {
    const myvar = Variable().poll()

    return <box onDestroy={() => myvar.drop()} />
}