On Sat, Apr 30, 2011 at 11:18 PM, Rob Riggs <rob@pangalactic.org> wrote:
On 04/30/2011 06:55 AM, Olaf van der Spek wrote:
exceptions are for exceptional cases
That oft-used bromide lacks any useful information about when the use of exceptions is appropriate.
Exceptions should be used (thrown) when contracts are violated or invariants cannot be maintained. The only time they should not be used in these cases is when checking the invariants would impact performance to such a degree that allowing undefined behavior may be preferable. And in this case, do what map and vector do: provide a checked and unchecked version.
A precondition for at() is that the key exists in the map. It is perfectly legitimate for at() to throw an exception for violating its precondition.
Of course. But I'm looking for a find wrapper. Find doesn't have such a precondition and the wrapper shouldn't have such a precondition either.
And /it is perfectly legitimate to make use of this behavior in one's code/. That is, there is nothing wrong with allowing an exception to be thrown if you can afford the stack unwinding.
Two bits of code:
if (foo.good()) { do_something_with(foo); }
and
try { do_something_with(foo); } catch (not_good&) {}
Both are valid. And sometimes the latter is most appropriate.
Personally, I tend to be more averse to functions that return bare pointers. Given the choice of a function that returns a bare pointer which may be NULL or using at() & try/catch, I would probably choose at() first.
I'd prefer the other way around. Olaf