[ruby-core:96702] [Ruby master Bug#11014] String#partition doesn't return correct result on zero-width match

[daniel@dan42.com]

Issue #11014 has been updated by Dan0042 (Daniel DeLorme).


IIRC this has to do with zero-length matches being ignored in certain conditions, in particular having to do with repeating/multiple matches.

if `"foo".split(/\A/)` was `["","foo"]`
then `"foo".split(//)` would have to be `["","f","o","o"]`
and `"foo".split(/\G/)` could result in infinite loop matching `["","","","","",..."foo"]`

But I don't understand why `partition` doesn't behave like `match`.

Note that gsub has different behavior:
`"foo".gsub(/\G/,'_') #=> "_f_o_o_"`
`"foo".gsub(//,'_') #=> "_f_o_o_"`

explained better than I ever could:
https://www.regular-expressions.info/zerolength.html

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Bug #11014: String#partition doesn't return correct result on zero-width match
https://bugs.ruby-lang.org/issues/11014#change-83688

* Author: janko (Janko Marohnić)
* Status: Assigned
* Priority: Normal
* Assignee: matz (Yukihiro Matsumoto)
* Target version: 
* ruby -v: ruby 2.2.1p85 (2015-02-26 revision 49769) [x86_64-darwin14]
* Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN, 2.2: UNKNOWN
----------------------------------------
First, to see how `String#match` works on my example:

~~~ruby
match = "foo".match(/^=*/)
match.pre_match  #=> ""
match[0]         #=> ""
match.post_match #=> "foo"
~~~

Now, if I used `String#partition` instead of `match`, I'd expect to get `["", "", "foo"]` (pre_match, match, post_match). However

~~~ruby
"foo".partition(/^=*/) #=> ["foo", "", ""]
~~~

`String#rpartition` returns the correct result (with the same regex).



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