Previous value of an Atom

[slimshader]

Hey, Is there a way to get previous value of an [Atom] property inside of Reaction?

[vanifatovvlad]

No, there is no way get the previous value of an atom. Alternatively, you can write reaction that remembers the previous value.

private void Start()
{
    Reaction(
        () => Counter,
        (current, previous) => Debug.Log($"Counter changed from {previous} to {current}")
    );
}

private static Reaction Reaction<T>(AtomPull<T> reaction, Action<T, T> effect)
{
    var hasPrevious = false;
    var previous = default(T);
    return Atom.Reaction(reaction, value =>
    {
        if (hasPrevious)
        {
            effect(value, previous);
        }

        previous = value;
        hasPrevious = true;
    });
}

[slimshader]

No, there is no way get the previous value of an atom. Alternatively, you can write reaction that remembers the previous value.

private void Start()
{
    Reaction(
        () => Counter,
        (current, previous) => Debug.Log($"Counter changed from {previous} to {current}")
    );
}

private static Reaction Reaction<T>(AtomPull<T> reaction, Action<T, T> effect)
{
    var hasPrevious = false;
    var previous = default(T);
    return Atom.Reaction(reaction, value =>
    {
        if (hasPrevious)
        {
            effect(value, previous);
        }

        previous = value;
        hasPrevious = true;
    });
}

Thanks! Btw, I want to use it to find the difference of 2 collections so that the view layer could efficiently update it's contents. I am trying to replace UniRx-based view models with [Atom]-based.