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Re: Back/front methods for Iterable (and reverse iterators)

 

What about:

selectWinners: func (clients: List<Client>) {
  deluxeLimit := 10
  winners := ArrayList<Client> new()
  losers := ArrayList<Client> new()

  winners addRange(clients take(deluxeLimit))
  losers addRange(clients skip(deluxeLimit))
}

On Fri, May 28, 2010 at 11:31 PM, Amos Wenger <amoswenger@xxxxxxxxx> wrote:

> (damn Enter key that sends in GMail..)
>
>
> The 'iterators are iterable' idiom is particularly useful in cases like
> that:
>
> selectWinners: func (clients: List<Client>) {
>   iter := clients forward()
>   deluxeLimit := 10
>   winners := ArrayList<Client> new()
>   losers := ArrayList<Client> new()
>
>   for(c in iter) {
>     winners add(c)
>     if(winners size() >= deluxeLimit) break
>   }
>
>   // continue attributing people.
>   for(c in iter) {
>     losers add(c)
>   }
> }
>
> Amos
>
>
> On Fri, May 28, 2010 at 11:29 PM, Amos Wenger <amoswenger@xxxxxxxxx>wrote:
>
>> Maybe we should have
>>
>>    - iterator()
>>    - backIterator() (can throw exception if unsupported)
>>    - forward() == iterator()
>>    - backward() == backIterator() reverse()
>>
>> The 'iterators are iterable' idiom is particularly useful in cases like
>> that:
>>
>> selectWinners: func (c: List<Clients>) {
>> deluxeLimit := 10
>>
>>
>> On Fri, May 28, 2010 at 10:20 PM, Noel Cower <ncower@xxxxxxxxx> wrote:
>>
>>> I like Josh and Rubin's ideas, although I think forward and backward
>>> don't really communicate that the iterator is going to be at one end or the
>>> other of the list.  Not all iterables are going to have the ability to go
>>> forward/backward, so it would make sense, to me at least, to put those in
>>> List, but then things like HashMap, which are iterable and can have reverse
>>> iteration, won't have those methods.
>>>
>>> Maybe another subclass of Iterable is necessary to give List and HashMap
>>> the same backing without having them be treated as different in terms of
>>> their ability to iterate forwards/backwards?  Like BidirectionalIterable or
>>> EndedIterable (the former being too long and the latter seems a little odd
>>> to me).
>>>
>>> If we do use forward/backward, should backward always be a reverse
>>> iterator?
>>>
>>> Also, iterable iterators sound nice, and I don't really see why we ought
>>> to not do that - wouldn't cost anything, just have the iterator return
>>> itself when iterator() is called.
>>>
>>>  -noel
>>>
>>> On May 28, 2010, at 9:48 AM, Amos Wenger wrote:
>>>
>>> I like the proposal of Rubin.
>>>
>>> Maybe iterator should be iterable? (they would just return themselves)
>>>
>>> In that case we could write:
>>>
>>> for(element in list backward())
>>>>
>>>
>>> And ex-Java programmers could even write
>>>
>>> for(element in list forward())
>>>>
>>>
>>> If they wanted.
>>>
>>> Amos
>>>
>>> On Fri, May 28, 2010 at 5:59 PM, cd rubin <launchpad@xxxxxxxxxxxxxxxx>wrote:
>>>
>>>>
>>>> Hey all
>>>>
>>>> In which case shouldn't the methods be called 'forwards' and
>>>> 'backwards'? I think that fits better with the language :
>>>>
>>>> "iterate over a list backwards"
>>>>
>>>> iter := list backwards()
>>>>
>>>> and it removes possible confusion stemming from calling the method
>>>> 'front' and getting an iterator instead of the first item of the list!
>>>>
>>>>  - Daniel (cdrubin)
>>>>
>>>> On Fri, May 28, 2010 at 11:21 AM, Josh Roesslein <jroesslein@xxxxxxxxx>wrote:
>>>>
>>>>> Bart makes a good point that not all Iterables will have an ordered
>>>>> structure (ex: socket input/output streams).
>>>>> I think it would make more sense having front() and back() methods in
>>>>> List that returns Iterators that either traverse
>>>>> the list head to tail or vice versa.
>>>>>
>>>>> Josh
>>>>>
>>>>> On Fri, May 28, 2010 at 9:33 AM, Amos Wenger <amoswenger@xxxxxxxxx>wrote:
>>>>>
>>>>>> So what then? iterator~back() ?
>>>>>>
>>>>>>
>>>>>> On Fri, May 28, 2010 at 2:53 PM, Bart van der Werf <
>>>>>> bluelive@xxxxxxxxx> wrote:
>>>>>>
>>>>>>> I'm not sure.
>>>>>>>
>>>>>>> Alot of iterables have no order, so if front/back is the default way
>>>>>>> to get an iterator it would make little sense.
>>>>>>>
>>>>>>
>>>>>>
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>>>>>>
>>>>>
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>>>>
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>>
>
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