Union of lifetime

[dmitry-bym]

Background and Motivation

Again lifetimes is awesome so i integrated that everywhere and i have activatable view models. Basicaly its same aproach but to force deactivate view. And I came across that in some places I would like to use same view model so i want deactivate that only when no one use this.

public interface IActivatableViewModel
{
    public void Activate(Lifetime lifetime);
}

2nd example
I have gpsService which track location and i want to stop tracking only when no one use this

public interface IGpsLocation
{
    public IObservable<Location> TrackLocation(Lifetime lifetime);
}

Proposed API

In order to provide a way to dispose that definition need to create spicific definition

public class UnionLifetimeDefinition(Lifetime parentLifetime)
{
    public Lifetime Lifetime { get; }
    public void Add(Lifetemi lifetime);
}

Alternative Designs

I thought about same approach like with Intersection, but its not good due to the fact that will not have a way to terminate that. Smth like add method Union and DefineUnion to lifetime. Basicaly same stracture as with Intersection

    public Lifetime Union(Lifetime other) => Union(this, other);

    public static Lifetime Union(params Lifetime[] lifetimes);

    public static LifetimeDefinition DefineUnion(params Lifetime[] lifetimes);

but it not possible to terminate same way, for intersection its possible to use global lifetime in the same place

var lf = Lifetime.Intersection(globalLifetime, localLifetime1, localLifetime2);