Extensions-for-ObservedRemoveSet.cs

public static class Extensions
{
    public static TValue GetOrNew<TKey, TValue>(this Dictionary<TKey, TValue> dict, TKey key)
        where TKey : notnull
        where TValue : new()
    {
        if (!dict.TryGetValue(key, out var value))
        {
            dict[key] = value = new();
        }

        return value;
    }
    
    public static void AddOrUpdateDot<TActorId>(this List<Dot<TActorId>> dots, TActorId actorId, int newVersion)
        where TActorId : IEquatable<TActorId>
    {
        var index = -1;
        for (var i = 0; i < dots.Count; ++i)
        {
            if (dots[i].Actor.Equals(actorId))
            {
                index = i;
                break;
            }
        }

        if (index < 0)
        {
            dots.Add(new Dot<TActorId>(actorId, newVersion));
        }
        else
        {
            dots[index] = new Dot<TActorId>(actorId, newVersion);
        }
    }
}