[Question] listening for changes on an observed node about anchors

[thehabbos007]

If you wanted to try to help hack on it, I think maybe the best way to solve it is to refactor the current mark_observed and mark_unobserved functions into a kind of Observer object

I'll try to play around with this idea. Would be a nice learning experience for myself as well :)

[lord]

I think you can actually do this already without any changes to Anchors, although perhaps it can be made more ergonomic? Just added this as example/update_callback.rs:

use anchors::expert::{AnchorExt, Var};
use anchors::singlethread::*;
use std::cell::RefCell;

fn main() {
    let mut engine = Engine::new();
    let (cat_count, set_cat_count) = Var::new(1);
    let (dog_count, set_dog_count) = Var::new(1);
    let (fish_count, set_fish_count) = Var::new(1);
    let total_mammals = (&cat_count, &dog_count).map(|cats, dogs| cats + dogs);
    let total_animals = (&total_mammals, &fish_count).map(|mammals, fish| mammals + fish);
    let mammal_callback = total_mammals.map(|total_mammals| println!("mammals updated: {:?}", total_mammals));
    let animal_callback = total_animals.map(|total_animals| println!("animals updated: {:?}", total_animals));
    engine.mark_observed(&mammal_callback);
    engine.mark_observed(&animal_callback);

    println!("stabilizing...");
    engine.stabilize();

    set_cat_count.set(2);
    set_dog_count.set(2);
    println!("stabilizing...");
    engine.stabilize();

    set_fish_count.set(2);
    println!("stabilizing...");
    engine.stabilize();
}

[lord]

Hey, sorry, just saw this! Would definitely be a great feature to add, thanks for the suggestion! I'll try to get to it in a couple days.

[thehabbos007]

It's all good! I was interested in helping out too, but I don't know if i understand the architecture well enough :)

Thank you a lot!

[lord]

If you wanted to try to help hack on it, I think maybe the best way to solve it is to refactor the current mark_observed and mark_unobserved functions into a kind of Observer object, and maybe allow subscribing to changes on that object? Kind of a vague suggestion, sorry.

Glad somebody out there is actually using this library, and sorry for the poor documentation!

[thehabbos007]

Ah, I see, of course using map would be a way to accomplish this.
What I had played around with was adding a callback function to the var new method and called it new_observed having that take in a callback closure which was added onto the returned Var. I'd then call down to that callback in poll_updated. Although it does work, it required a lot of finicky type declarations to make the compiler happy, not really a solution I liked.

This is more sensible :)

[lord]

Ah, nice! Glad this works for you, and thanks again for submitting this feedback.

Will close this issue, but if you have other ideas for improvements, would love to hear them! Feel free to open as many issues as you'd like.