associative arrays: iteration is finally here

[Andrei Alexandrescu]

Leandro Lucarella wrote:
> Andrei Alexandrescu, el 29 de octubre a las 12:33 me escribiste:
>> Bill Baxter wrote:
>>>> 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
> 
> I don't agree, this is like saying you should bound-check every array
> access. I think it's nice to have safety by default.

remove from an associative array is not unsafe.

> If you are expecting
> to have an error, you will be extra careful to spell the key correctly.
> This should cover the cases where you are distracted and not expecting any
> errors.
> 
> I think the check could be done in non-release mode only though, just
> like bound checking.

Bounds checking is eliminated in release mode solely for efficiency 
reasons. There is no other good reason to eliminate checks. But in the 
case of remove, the amount of work done is consistent enough to make a 
check negligible.

>> 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.
> 
> This is one case where I think practicality beats purity, because the
> whole point of throwing an exception is for the cases you don't expect it
> to fail. Again, think of array bounds, you can force the programmer to add
> lots of enforce() in the code and remove bound checking from the compiler.

I can't think of array bounds. The situations are completely unrelated.


Andrei