Question

The Exception is a convenient container, that is tempting to use for various purposes. But is it OK to use it for handling legal states in your code?

My example: I have a geometric function that finds the closest object within a search radius:

public IPoint FindNearest(IPoint origin, double searchRadius)
{

}

My idea was that I could throw an exception, when the search doesn’t find a hit. But is this a good idea? Alternatively, I could return Null (which I don’t like), or return a result object instead of a Point.

Answer 1

Usually in this situation throwing exceptions isn’t a good idea, they are expensive and semantically mean something else entirely.

You could return null and do a null check, or I occasionally find that using the Special Case pattern works out nicely and makes for readable code if you give the class/interface a sensible name.

In this instance, you’d return either an implementing class or derived interface called something like:

public class NoHitOnRadius : IPoint {}

And return that from the call when you get no hits. Then the calling code checks the return type:

var p = FindNearest(...);

if (p is NoHitOnRadius) 
{
    // Do something.
}

Although in this specific situation I’d likely go with the TryFindNearest semantics (to keep commonality with the likes of TryParse etc) that RobH suggests.