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copied!<p>One thing I've learned working with .NET (and with some people who are quick to jump to a hack solution) is that if nothing else, reflection will often allow people to by pass your "protections." </p> <p>Interfaces are not iron shackles of programming, they're a promise that your code makes to any other code saying "I can definitely do these things." If you "cheat" and cast the interface object into some other object because you, the programmer, know something that the program doesn't, then you're breaking that contract. The consequence is poorer maintainability and a reliance that no one ever mess up anything in that chain of execution, lest some other object get sent down that doesn't cast correctly.</p> <p>Other tricks like making things readonly or hiding the actual list behind a wrapper are only stop-gaps. You could easily dig into the type using reflection to pull out the private list if you really wanted it. And I think there are attributes you can apply to types to prevent people from reflecting into them.</p> <p>Likewise, readonly lists aren't really. I could probably figure out a way to modify the list itself. And I can almost certainly modify the items on the list. So a readonly isn't enough, nor is a copy or an array. You need a deep copy (clone) of the original list in order to actually protect the data, to some degree.</p> <p>But the real question is, why are you fighting so hard against the contract that <em>you wrote</em>. Sometimes reflection hacking is a handy workaround when someone else's library is poorly designed and didn't expose something that it needs to (or a bug requires that you go digging to fix it.) But when you have control over the interface AND the consumer of the interface, there's no excuse to not make the publicly exposed interface as robust as you need it to be to get your work done.</p> <p><strong>Or in short:</strong> If you need a list, don't return IEnumerable, return a List. If you've got an IEnumerable but you actually needed a list, then its safer to make a new list from that IEnum and use that. There are very few reasons (and even fewer, maybe no, good reasons) to cast up to a type simply because "I know it's actually a list, so this will work." </p> <p>Yeah, you can take steps to try and prevent people from doing that, but 1) the harder you fight people who insist on breaking the system, the harder they will try to break it and 2) they're only looking for more rope, and eventually they'll get enough to hang themselves.</p>

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