Why Strings as Classes? [C++ iterator]

[David Wilson]

2008/8/28 Fawzi Mohamed <fmohamed at mac.com>:
> On 2008-08-28 00:24:50 +0200, Dee Girl <deegirl at noreply.com> said:
>
>> Derek Parnell Wrote:
>>
>>> On Wed, 27 Aug 2008 17:08:47 -0400, Nick Sabalausky wrote:
>>>
>>>> The way I see it, encapsulation is all about the black box idea. And the
>>>> only things you can see from outside the black box are the inputs and
>>>> outputs.
>>>
>>> Well said.
>>
>> I am sorry I will say my opinion. This sounds good but is simplistic.
>> Black box is good in principle. But it assume you found right interface for
>> the black box. If you define bad interface you have a bad black box. Also
>> please remember that iterator is black box also. But it defines right
>> interface.
>
> I agree with the meaning, but I disagree with the example.
> I think that iterators are an example of bad interface, as also others
> brought up the iterator as good example I though that I should say
> something.
>
> An iterator should be like a generator, have a method next, and one at_end
> or something similar packaged (and maybe prev() and at_start() if it can
> also go back) in a single struct, furthermore it should work seamlessly with
> a kind of for_each(x;iterator) construct.
>
> Instead C++ choose to have begin & end iterators, simply because with that
> construct it is trivial for the compiler to optimize it for arrays, and you
> can use pointers as iterators without a cast/constructor.
>
> This means a worse interface for 99% of the uses, apart form arrays and
> vectors I think one is better off without end iterator, and even when this
> is not the case writing something like for_each(x;FromTo(a,b)), with FromTo
> constructing a generator is (I think) better than
> for(i=t.begin();i!=t.end();++t), and the implementation of an a generator
> itself is easier (no ==,!=,increment, decrement(pre/post),... for
> performance reasons)

It is worse in simple "for each element" uses, but one of the cooler
things about C++ iterators is exactly that they are exchangeable for
any pointer-like object, and that it's trivial to iterate over a
subset of a container. Emulating pointers means that in some ways,
once you grok how they work, they are more trivial than e.g. Python or
D since there is no further specialised syntax beyond "*", "++", and
maybe "--".

I love the concise D and Python syntaxes, just playing devil's advocate here. :)


>
> As I believe that the optimizations to make the better interface be as
> efficient as the iterator one are perfectly doable (some work, yes, but not
> extremely much so), I see no good reason for C++ design.
>
> Fawzi
>
>