Question

I’m trying to debug my code which is being executed from a unit test project, but when I try to step into a method, it just passes straight onto the next line and the breakpoint inside that method isn’t hit. The method is on a class which is in a different project, but all the code is built in debug mode and I’ve tried cleaning and rebuilding the solution with no joy.

However, this has only happened since I added an iterator block to the method. When I remove it and rebuild, I can step in fine. Weird?

I am using Visual Studio 2010 Beta 1, could this just be a bug?

Answer 1

Iterator blocks use deferred execution – meaning: until you actually start iterating over the data, nothing is executed.

So: has the data been iterated? Is anything looping over the values? If you need to add validation logic that runs as early as possible, you currently need two methods:

public static IEnumerable<int> GetNumbers(int from, int to) {
    // this validation runs ASAP (not deferred)
    if (to < from) throw new ArgumentOutOfRangeException("to");
    return GetNumbersCore(from, to);
}
private static IEnumerable<int> GetNumbersCore(int from, int to) {
    // this is all deferred
    while (from <= to) {
        yield return from++;
    }
}