associative arrays: iteration is finally here

[Andrei Alexandrescu]

Bill Baxter wrote:
> On Thu, Oct 29, 2009 at 8:39 AM, Andrei Alexandrescu
> <SeeWebsiteForEmail at erdani.org> wrote:
>> Leandro Lucarella wrote:
>>> Andrei Alexandrescu, el 28 de octubre a las 20:29 me escribiste:
>>>>>> Your test looks something up and then removes it.
>>>>>>
>>>>>>
>>>>>> Andrei
>>>>> Well, my extended test case looks something up, manipulates the
>>>>> found value, and then possibly removes it.
>>>> Ok, I understand your points, thanks for explaining.
>>> What about and overload of remove() like this:
>>> bool remove(in T key, out U value);
>>>
>>> If the element was present, it's returned in "value", so you can
>>> manipulate it. I thought about just returning a pointer:
>>> U* remove(in T key);
>>>
>>> But I guess that pointer would point to the element stored in the the AA
>>> private data, but that element was just removed, so bad things would
>>> happen, that's why the only option is to copy the data, right?
>> I think this all is overdoing it. First, I disagree that remove should ever
>> throw an exception. It's not a code that the user is supposed to check (with
>> dire consequences if she doesn't), it's just additional information just in
>> case you need it.
>>
>> I think bool remove(key) is better than all other designs suggested so far.
> 
> I agree with the folks who say it's error-prone.  I can just see
> myself now removing a key I know is in the dictionary and being
> baffled when my program fails somewhere later on because I typed
> aa.remove("theKey") when it should have been aa.remove("thekey").  I
> knew it was there so I didn't want to clutter up my code with a check
> for it.

I don't find this reasonable. If you know removal must have succeeded, 
just type enforce(aa.remove("theKey")). I don't think that's the 
overwhelmingly common case though, and if it's, say, about 50/50, then 
it's much more sensible to have a non-throwing primitive than a throwing 
one. And it looks like defining two primitives just to save a call to 
enforce is not a good design. After all, if you argue people forget and 
misspell things and all, I could argue they call the wrong function out 
of two with very similar charters. Honest, I just read a couple of posts 
proposing two primitives and for the life of me I already can't remember 
which was throwing and which wasn't.

> So the advice would be to always check to make sure the key you remove
> got removed to be on the safe side.

I'm not seeing how that comes about. The advice is to check if you care, 
which is common sense. I'm wondering how such an obvious design came 
into question.


Andrei