I tend to agree Dawid.
Especially the comparison with Python behaviour is demonstrative.
Is there any spec weather the Java Regex API has a general contract with 16-bit chars or Unicode
codepoints?
Thinking about the search pattern e.g. "[AB\uD840\uDC00C]"; what does it actually search for, the
isolated occurence of each char, or the occurence of the codepoint "\uD840\uDC00" ?
Last, but not least, we should think about, which would be the common use case, an which would be
more easy to work around.
(I think, the current view on isolated chars is more easy to work around:
StringBuilder sb = new StringBuilder(s1.length + 1).append('X');
for (char c : s1.getChars())
sb.append(c).append('X');
String s2 = sb.toString();
)
Additionally I like to discuss: "any possible zero-width position of the target
String"
If String length is l, maybe it's arguable, that position l is no valid
position in the String.
From the use case point of view, I think "P e t e r" as result of "Peter".replaceAll("", " ") is
the most useful.
-Ulf
Am 08.06.2012 13:14, schrieb Dawid Weiss:
I guess a lot depends on the point of view. From historical point of
view (where a char[] and a String are basically unsigned values) that
pattern should simply process every value (index) and work like you
say. But from a practical point of view I think it is a bug -- it
corrupts the string, transforming legal unicode into invalid values.
I checked with Python (3) and the behavior there is the expected one
(it work at the unicode codepoint level rather than surrogate level).
Where is the behavior of "" that you mention defined? I admit I
couldn't find any reference to this in the documentation:
Using an empty String "" as a regex for the replaceAll() takes the
advantage of the special meaning of "", in which it is interpreted as
it can match any possible zero-width position of the target String
I'm not saying you're wrong (and that pattern is definitely not common
so it's probably academic discussion) but I'd like some concrete
reference as to how an empty pattern should behave. To me consistency
with the rest of the Pattern specification would be that it operates
at "zero width position between unicode characters" not between any
char[] value, even an incorrect one or in the middle of a surrogate.
Dawid
On Fri, Jun 8, 2012 at 12:46 AM, Xueming Shen<xueming.s...@oracle.com> wrote:
Personally I don't think it is a bug. A j.l.String represents a sequence of
UTF-16 chars. While
a pair of surrogates represents a supplementary character, a single
surrogate itself is still
a "legal" independent entity inside a String object and length of a String
is still defined as
the total number of char unit and an index value between a high surrogate
and a low
surrogate is still a legal index value that can be used to access the char
at that particular
position. Using an empty String "" as a regex for the replaceAll() takes the
advantage of the
special meaning of "", in which it is interpreted as it can match any
possible zero-width
position of the target String, it does not imply anything regarding
"character" or
"characters" around it, so I would not interpret it as a zero-with character
boundary,
therefor a "position" in between a pair surrogates is still a good "found"
for replacing.
-Sherman
On 6/7/2012 1:07 PM, Dawid Weiss wrote:
Hi, I'm a committer to the Apache Lucene project. We have randomized
tests and one seed hit the following (simplified) scenario:
String s1 = "AB\uD840\uDC00C";
String s2 = s1.replaceAll("", "X");
the input contains an extended unicode character (any surrogate pair
will do). The pattern is an empty string (in fact, it was randomized
as "]|" but it's the same problem so I omit the details). The problem
is that after applying this pattern, replaceAll inserts X in between
the surrogate pair characters and this results in invalid UTF-16:
AB𠀀C
XAXBX?X?XCX
I believe this is a bug in the regexp implementation (sorry, don't
have a patch for it) but I'd like to confirm it's not something known.
Pointers appreciated.
Dawid
