Re: Assertion vs Exception Handling
Chris Gordon-Smith<use.address@my.homepage.invalid> wrote:
James Kanze <james.kanze@gmail.com> wrote:
Whether exception handling or assertions are more appropriate
depends on the type of error and the application domain. And
possibly other considerations as well.
I would be interested to know whether there are any guidelines on
this. It seems to me that exceptions are often useful in cases where
the program itself has done nothing wrong, but something unusual has
happened in its environment.
My basic guideline is that a catch should always re-throw, because if
your program can recover from the situation, then it isn't an error.
When writing a function, if a precondition is violated, then an error
has been detected in the calling code, an error that this function
cannot fix (by definition.) Unless you know for a fact that every
program that could possibly use this function should abort whenever a
precondition is violated, without any chance to save data or otherwise
clean up, you should not use 'assert', throw an exception instead.
If a postcondition is violated, then the function was written
incorrectly. Chances are, you didn't write either an assert or exception
to cover such an issue, because if you knew the function wouldn't work,
you would have fixed the code rather than adding code to notify the
caller that your code is broken. Whenever a postcondition violation
takes place, you should fix the code so it can't happen anymore. It
would not be appropriate to leave the bug in and add an assertion or
exception to notify the caller that your code doesn't work.