Exceptions for flow of control

Question

There is an interesting post over here about this, in relation to cross-application flow of control.

Well, recently, I've come across an interesting problem. Generating the nth value in a potentially (practically) endless recursive sequence. This particular algorithm WILL be in atleast 10-15 stack references deep at the point that it succeeds. My first thought was to throw a SuccessException that looked something like this (C#):

class SuccessException : Exception
{
    public string Value
    { get; set; }

    public SuccessException(string value)
        : base()
    {
        Value = value;
    }
}

Then do something like this:

try
{
    Walk_r(tree);
}
catch (SuccessException ex)
{
    result = ex.Value;
}

Then my thoughts wandered back here, where I've heard over and over to never use Exceptions for flow control. Is there ever an excuse? And how would you structure something like this, if you were to implement it?

Answer 1

In this case I would be looking at your Walk_r method, you should have something that returns a value, throwing an exception to indicate success, is NOT a common practice, and at minimum is going to be VERY confusing to anyone that sees the code. Not to mention the overhead associated with exceptions.