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    <p>By definition, "exception" means an exceptional circumstance from which a routine cannot recover. In the example you provided, it looks like that means the image was invalid/corrupt/unreadable/etc. That should be thrown and bubbled up to the topmost layer, and <em>there</em> decide what to do with the exception. The exception itself contains the most complete information about what went wrong, which must be available at the upper levels.</p> <p>When people say you should not use exceptions to control program flow, what they mean is: (for example) if a user tries to create an account but the account already exists, you should not throw an AccountExistsException and then catch it higher up in the application to be able to provide that feedback to the user, because the account already existing is not an exceptional case. You should expect that situation and handle it as part of your normal program flow. If you can't connect to the database, <em>that</em> is an exceptional case.</p> <p>Part of the problem with your User Registration example is that you are trying to encapsulate too much into a single routine. If your method tries to do more than one thing, then you have to track the state of multiple things (hence things getting ugly, like lists of error messages). In this case, what you could do instead is:</p> <pre><code>UsernameStatus result = CheckUsernameStatus(username); if(result == UsernameStatus.Available) { CreateUserAccount(username); } else { //update UI with appropriate message } enum UsernameStatus { Available=1, Taken=2, IllegalCharacters=3 } </code></pre> <p>Obviously this is a simplified example, but I hope the point is clear: your routines should only try to do one thing, and should have a limited/predictable scope of operation. That makes it easier to halt and redirect program flow to deal with various situations.</p>
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    1. POHow does code look when you don't use exceptions to control flow?
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    1. USRex M
    1. USRex M
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    1. POHow does code look when you don't use exceptions to control flow?
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    1. COCheck out my last snippet. Is that something that would warrant a thrown exception?
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      1. USNick Swarr
    2. CONo, not an exceptional case. You should handle something like a username already in use as part of your business logic using something like a BrokenRules collection.
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      1. USJasonS
    3. CORex, for the user registration method, it's at the level of the orchestration of creating a new account. Part of that orchestration is validating the health of the account and then passing it on to the appropriate persistent store. Assume that there is no username check. We only validate the state of the account before saving it. How do I relate the state errors back to the client? Is the recommendation to push the validation up to a higher level module (in this case, a controller)?
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