Question

I’d like to try something every second for five seconds, return false if they are all false, and return true the first time one is true. Imperatively, it’d look like this:

bool TryFiveTimes()
{
    for (int i = 0; i < 5; i++)
    {
        if (Fn())
            return true;
        System.Threading.Thread.Sleep(1000);
    }
    return false;
}

I’d like to do this using Rx, but can’t think of a neat way. My current attempt is:

bool TryFiveTimes()
{
    return Observable.Interval(TimeSpan.FromSeconds(1))
        .Take(5)
        .Select(_ => Fn())
        .Scan(false, (curr, prev) => curr || prev)
        .Last();
}

This will give the correct result, but won’t return early if Fn() returns true before the end.

Answer 1

You could try using Concat with Return like this:

bool TryFiveTimes()
{
    return Observable
        .Interval(TimeSpan.FromSeconds(1))
        .Take(5)
        .Select(_ => Fn())
        .Where(x => x)
        .Concat(Observable.Return(false))
        .First();
}