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

[Paul Sandoz]

Following on from this are the idiomatic stream creation methods, we have previously discussed:

  IntStream.ints();
  LongStream.longs();
  DoubleStream.doubles();

Half-open, or closed? I think a closed range would be the most likely expectation, and could be implemented using rangeClosed.

doubles() would be restricted to [0.0, 2.0^53].

Paul.

On May 2, 2013, at 9:41 PM, Paul Sandoz <Paul.Sandoz at oracle.com> wrote:

> Hi,
> 
> Any thoughts below on the following? use-cases? experiences?
> 
> Paul.
> 
> --
> 
> At the moment we have the {Int, Long, Double}Stream.range methods for a half open range of a step of 1 or a configurable step >= 0.
> 
> Do we really require the configurable step methods? Perhaps they are not that common, if so should we remove them?
> 
> Certainly one can achieve a step > 1 using map(i -> i * n), albeit less efficiently. Note that this will not check for overflow when the upper bound declared to be the maximum value.
> 
> -- 
> 
> The fact that we only have a half open range confuses some. Developers i think tend to prefer:
> 
>  IntStream.rangeClosed('A', 'Z')
> 
> rather than:
> 
>  IntStream.range('A', 'Z' + 1)
> 
> So it seems useful to add {Int, Long}Stream.rangeClosed().
> 
> --
> 
> Do we require a method for descending ranges, for example {Int, Long}Stream.rangeDec? what about for closed descending ranges?
> 
> Again those can be achieved using map, albeit less efficiently and with overflow errors, and perhaps developers will make simple errors expressing the mapping?
> 
> --
> 
> For DoubleStream.range i think supporting +ve/-ve steps is useful e.g. [0, 2 * pi, pi / 180] and [2 * pi, 0, -pi / 180]
> 
> Should the range always be closed, half open or both? 
> 
> Half open ranges for Int/Long make sense because of the correlation with array indexes.
> 
> --
> 
> Should we support sizes for LongStream.range that are > Long.MAX_VALUE? for example:
> 
>  LongStream.range(Long.MIN_VALUE, Long.MAX_VALUE)
> 
> The top-level Spliterator of such a stream cannot report SIZED or SUBSIZED and would report an estimate of Long.MAX_VALUE.
> 
> DoubleStream.range is restricted to a maximum of Long.MAX_VALUE. This simplifies the implementation, since it is equivalent to:
> 
>  double size = Math.ceil((endExclusive - startInclusive) / step);   
>  LongStream.range(0, (long) size).mapToDouble(i -> startInclusive + i * step);
> 
> and a simplified version of the long range spliterator is used.
>