`encoding` can be not only an encoding name, but also an Encoding object.
```
s = String.new('foo', encoding: Encoding::US_ASCII)
s.encoding # => #<Encoding:US-ASCII>
```
If the passed string is frozen, bare and not shared, then there
is no need to duplicate it.
Ref: 4ab69ebbd7cef8539f687e1f948845d076461dc6
Ref: https://bugs.ruby-lang.org/issues/11386
When the pattern Regexp given to String#index and String#rindex
contain a /\K/ (lookbehind) operator, these methods return the
position where the beginning of the lookbehind pattern matches, while
they are expected to return the position where the \K matches.
```
# without patch
"abcdbce".index(/b\Kc/) # => 1
"abcdbce".rindex(/b\Kc/) # => 4
```
This patch fixes this problem by using BEG(0) instead of the return
value of rb_reg_search.
```
# with patch
"abcdbce".index(/b\Kc/) # => 2
"abcdbce".rindex(/b\Kc/) # => 5
```
Fixes [Bug #17118]
When the pattern given to String#partition and String#rpartition
contain a /\K/ (lookbehind) operator, the methods return strings
sliced at incorrect positions.
```
# without patch
"abcdbce".partition(/b\Kc/) # => ["a", "c", "cdbce"]
"abcdbce".rpartition(/b\Kc/) # => ["abcd", "c", "ce"]
```
This patch fixes the problem by using BEG(0) instead of the return
value of rb_reg_search.
```
# with patch
"abcdbce".partition(/b\Kc/) # => ["ab", "c", "dbce"]
"abcdbce".rpartition(/b\Kc/) # => ["abcdb", "c", "e"]
```
As a side-effect this patch makes String#partition 2x faster when the
pattern is a costly Regexp by performing Regexp search only once,
which was unexpectedly done twice in the original implementation.
Fixes [Bug #17119]
Use BEG(0) instead of the result of rb_reg_search to handle the cases
when the separator Regexp contains /\K/ (lookbehind) operator.
Fixes [Bug #17113]
Not every compilers understand that rb_raise does not return. When a
function does not end with a return statement, such compilers can issue
warnings. We would better tell them about reachabilities.
After the encoding index instance variable is removed when all
instance variables are removed in `obj_free`, then `rb_str_free`
causes uninitialized instance variable warning and nil-to-integer
conversion exception. Both cases result in object allocation
during GC, and crashes.
Instead of searching twice to extract and to delete, extract and
delete the found position at the first search.
This makes faster nearly twice, for regexps and strings.
| |compare-ruby|built-ruby|
|:-------------|-----------:|---------:|
|regexp-short | 2.143M| 3.918M|
|regexp-long | 105.162k| 205.410k|
|string-short | 3.789M| 7.964M|
|string-long | 1.301M| 2.457M|
