ENH: Make use of RangeIndex in DatetimeIndex

[kawochen]

DatetimeIndex looks like it can benefit from RangeIndex #11892 .
Use case 1: Evenly-spaced time-series analysis
Use case 2: I sometimes (ab)use date_range like a PY3 range in a for loop, which I think is quite neat. It would be cooler if it were lazily evaluated.

[jreback]

@kawochen absolutely for 1 (might not even be that tricky as would simply need to move to sub-class from Int64Index to RangeIndex

can you give a more full example for 2)?

[kawochen]

For 2) I just meant

for d in date_range('20110101', '20121225'):
    process(d)

It's much better than updating with some time delta, and quacks like datetime.datetime enough that it serves all needs I have for the latter.
It solves this SO problem perfectly.

[jreback]

ah I c.

that brings up a good point actually. __iter__ is NOT lazy ATM for Int64Index, but for RangeIndex it certainly could/should be.

[max-sixty]

...and PeriodIndex!