Bug #12833
Updated by jonwolski (Jon Wolski) about 8 years ago
## Duplicate
This ticket duplicates [[https://bugs.ruby-lang.org/issues/12285]]
## Expected
`DateTime.iso8601('2016-10')` parses the input string as four-digit year and two-digit month.
```sh
$ ruby -r date -e "puts DateTime.iso8601('2016-10').iso8601"
2016-10-01T00:00:00+00:00
```
## Actual
`DateTime.iso8601('2016-10')` parses the input string as four-digit year and two-digit day-of-month.
```sh
$ ruby -r date -e "puts DateTime.iso8601('2016-10').iso8601"
2016-01-10T00:00:00+00:00
```
## Steps to reproduce
```sh
$ ruby -v -r date -e "puts DateTime.iso8601('2016-10').iso8601"
ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin15]
2016-01-10T00:00:00+00:00
```
## More details
```sh
$ ruby -r date -e "puts Date._iso8601('2016-10')"
{:mday=>10, :year=>2016}
$ ruby -r date -e "puts Date._iso8601('2016-101')"
{:yday=>101, :year=>2016}
```
This seems to suggest that the "10" is parsed as day-of-month (`:mday`) in the case of "YYYY-DD", but "101" is parsed as day-of-year (`:yday`) in the case of "YYYY-DDD". (The 3-digit day part _does_ in fact represent the day-of-year; that feature is correct.)