Debug.Assert vs Exception Throwing

Question

I\'ve read plenty of articles (and a couple of other similar questions that were posted on StackOverflow) about how and when to use assertions, and I understood the

Answer 1

I think a (contrived) practical example may help illuminate the difference:

(adapted from MoreLinq's Batch extension)

// 'public facing' method
public int DoSomething(List stuff, object doohickey, int limit) {

    // validate user input and report problems externally with exceptions

    if(stuff == null) throw new ArgumentNullException("stuff");
    if(doohickey == null) throw new ArgumentNullException("doohickey");
    if(limit <= 0) throw new ArgumentOutOfRangeException("limit", limit, "Should be > 0");

    return DoSomethingImpl(stuff, doohickey, limit);
}

// 'developer only' method
private static int DoSomethingImpl(List stuff, object doohickey, int limit) {

    // validate input that should only come from other programming methods
    // which we have control over (e.g. we already validated user input in
    // the calling method above), so anything using this method shouldn't
    // need to report problems externally, and compilation mode can remove
    // this "unnecessary" check from production

    Debug.Assert(stuff != null);
    Debug.Assert(doohickey != null);
    Debug.Assert(limit > 0);

    /* now do the actual work... */
}

So as Eric Lippert et al have said, you only assert stuff that you expect to be correct, just in case you (the developer) accidentally used it wrong somewhere else, so you can fix your code. You basically throw exceptions when you have no control over or cannot anticipate what comes in, e.g. for user input, so that whatever gave it bad data can respond appropriately (e.g. the user).