The Right Approach to Exceptions

Andrei Alexandrescu SeeWebsiteForEmail at
Sun Feb 19 00:02:39 PST 2012

On 2/19/12 12:54 AM, H. S. Teoh wrote:
> On Sun, Feb 19, 2012 at 12:43:58AM -0600, Andrei Alexandrescu wrote:
>> On 2/18/12 8:00 PM, H. S. Teoh wrote:
>>>>  From this and other posts I'd say we need to design the base exception
>>>> classes better, for example by defining an overridable property
>>>> isTransient that tells caller code whether retrying might help.
>>> Just because an exception is transient doesn't mean it makes sense to
>>> try again. For example, saveFileMenu() might read a filename from the
>>> user, then save the data to a file. If the user types an invalid
>>> filename, you will get an InvalidFilename exception. From an abstract
>>> point of view, an invalid filename is not a transient problem: retrying
>>> the invalid filename won't make the problem go away. But the application
>>> in this case *wants* to repeat the operation by asking the user for a
>>> *different* filename.
>>> On the other hand, if the same exception happens in an app that's trying
>>> to read a configuration file, then it *shouldn't* retry the operation.
>> I'm thinking an error is transient if retrying the operation with the
>> same exact data may succeed. That's a definition that's simple,
>> useful, and easy to operate with.
> [...]
> But if that's the case, what's the use of an exception at all?



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