ints(), longs(), doubles() <was> Re: Ranges

[Paul Sandoz]

Hi Howard,

I like the concept of a Range type and builder, although it might be too late to introduce a Range class now (there is nothing stopping us from adding it later).

In the Streams API the size of the range is important so that the range spliterator can produce balanced splits.

Paul.

On May 4, 2013, at 3:45 AM, Howard Lovatt <howard.lovatt at gmail.com> wrote:

> I write numerical code and find something like:
> 
>  from(start).to(exclusiveEnd).step(step).stream()...
> 
> with generalised to (whileTrue) and step variations, e.g.:
> 
>  from(start).whileTrue((i) -> i < limit).step((i) -> 2 * i).stream()...
> 
> useful in my in house library, it's great for paralleling existing loops! 
> 
> I implement it with something like this (I am using an in-house stream library so below is para-phrasing what I do):
> 
> public interface IntStream {
>  ...
>  class Range {
>    private int from = 0;
>    private IntPredicate whileTrue = (notUsed) -> true;
>    private IntFunction step = (i) -> i + 1;
>    public Range from(int from) { this.from = from; return this; }
>    public Range to(int exclusiveEnd) { whileTrue = (i) -> i < exclusiveEnd; return this; } 
>    public Range step(int step) { this.step = (i) -> i + 1; return this; }
>    public Range step(IntFunction step) { this.step = step; return this; }
>    public Range whileTrue(IntPredicate whileTrue) { this.whileTrue = whileTrue; return this; }
>    public IntStream stream() { ... }
>  }
>  static Range from(int from) { return new Range().from(from); }
>  static Range to(int exclusiveEnd) { return new Range().to(exclusiveEnd); }
>  static Range step(int step) { return new Range().step(step); }
>  static Range step(IntFunction step) { return new Range().step(step); }
>  static Range whileTrue(IntPredicate whileTrue) { return new Range().whileTrue(whileTrue); }
>  static IntStream stream() { return new Range().stream(); }
> }
> 
> -- Howard. 
> 
> Sent from my iPad
> 
> On 04/05/2013, at 3:35 AM, Tim Peierls <tim at peierls.net> wrote:
> 
>> On Fri, May 3, 2013 at 1:26 PM, Brian Goetz <brian.goetz at oracle.com> wrote:
>> 
>>> I don't think it would. While "indexes" does capture the essence of a
>>>> common use of this method, I think of [start, bound) as a range, and
>>>> would look it up under that name. range and rangeClosed are very similar
>>>> concepts; they should have similar names. The potential for confusion
>>>> doesn't seem that significant to me.
>>>> 
>>> 
>>> With two forms, I agree.  But the next two questions are:
>>> - what about decreasing ranges?
>>> - what about decreasing closed/half-open ranges (whichever the above
>>> isnt)?
>>> 
>>> Now, if the answer to these incremental questions is "you lose", then
>>> range and rangeClosed are fine, and we're done.
>>> 
>> 
>> All of these variations seem like things that aren't hard to roll for
>> yourself, especially with a few good examples in the javadoc.
>> 
>> But if range and rangeClosed really don't feel like enough to you, then
>> retain the stepped versions (with a different, uglier name) but add an
>> open/closed argument so it's only one extra method for each of the
>> primitive types and not two.
>> 
>>   rangeFarAfield(start, bound, step, HALF_OPEN);
>> 
>> Ugly enough that people won't use it unless they have to.
>> 
>> --tim
>