Pattern to avoid nested try catch blocks?

Question

Consider a situation where I have three (or more) ways of performing a calculation, each of which can fail with an exception. In order to attempt each calculation until we f

Answer 1

You can use a Task/ContinueWith, and check for the exception. Here's a nice extension method to help make it pretty:

    static void Main() {
        var task = Task.Factory.StartNew(Calc1)
            .OrIfException(Calc2)
            .OrIfException(Calc3)
            .OrIfException(Calc4);
        Console.WriteLine(task.Result); // shows "3" (the first one that passed)
    }

    static double Calc1() {
        throw new InvalidOperationException();
    }

    static double Calc2() {
        throw new InvalidOperationException();
    }

    static double Calc3() {
        return 3;
    }

    static double Calc4() {
        return 4;
    }
}

static class A {
    public static Task OrIfException(this Task task, Func nextOption) {
        return task.ContinueWith(t => t.Exception == null ? t.Result : nextOption(), TaskContinuationOptions.ExecuteSynchronously);
    }
}