enhanced for loop with multiple iteration variables

[forax at univ-mlv.fr]

----- Mail original -----
> De: "Alan Snyder" <javalists at cbfiddle.com>
> À: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "core-libs-dev" <core-libs-dev at openjdk.java.net>
> Envoyé: Vendredi 21 Décembre 2018 03:20:46
> Objet: Re: enhanced for loop with multiple iteration variables

> Lambdas are clean, but limited in current Java compared to nested blocks.
> 
> Are full featured lambdas on the horizon?

not in the immediate future, co-routine, sealed class, record, pattern matching, value type and reified generics are the next features.

> 
> If not, then we still need loops and iterators.
> 
>  Alan

Rémi

> 
> 
> 
> 
>> On Dec 20, 2018, at 3:00 PM, Remi Forax <forax at univ-mlv.fr> wrote:
>> 
>> or
>>  map.forEach((key, value) -> {
>>    ...
>>  });
>> 
>> Rémi
>> 
>> ----- Mail original -----
>>> De: "Brian Goetz" <brian.goetz at oracle.com>
>>> À: "Alan Snyder" <fishgarage at cbfiddle.com>, "core-libs-dev"
>>> <core-libs-dev at openjdk.java.net>
>>> Envoyé: Jeudi 20 Décembre 2018 23:50:15
>>> Objet: Re: enhanced for loop with multiple iteration variables
>> 
>>> For Map, you can do:
>>> 
>>>     for (Map.Entry<K,V> e : map.entrySet()) { ... }
>>> 
>>> and you're already there.
>>> 
>>> 
>>> 
>>> On 12/19/2018 9:54 AM, Alan Snyder wrote:
>>>> Has any consideration been given to supporting iterators that provide more than
>>>> one iteration variable in the enhanced for loop?
>>>> 
>>>> Obvious uses would be maps (keys and values) and lists (indexes and values).
>>>> 
>>>> I have in mind keeping the syntactic sugar approach by using one or more
>>>> extensions of the Iterator/Iterable interfaces, such as, for example:
>>>> 
>>>> interface Iterator2<E1,E2> extends Iterator<E1> {
>>>>   E2 get2();
>>>> }
>>>> 
>>>> with the extra methods providing the values for the extra variables (associated
>>>> with the previous call to next).
>>>> 
>>>> Extending interfaces is not required, but it makes the trailing variables
>>>> optional, which might be useful. For example, the same iterator could provide
>>>> values or values and keys.
>>>> 
>>>> The fact that this approach only works for a fixed set of numbers of variables
>>>> does not bother me unduly.
>>>> 
>>>>   Alan