On Tue, 11 Mar 2008 you wrote
Chris Hall skribis 2008-03-11 18:48 (+0000):
I'm comfortable with the notion that perl characters are unsigned
integers that overlap UCS, and happen to be held internally as a
superset of UTF-8.
I wonder if perl is completely comfortable.
It isn't. There are some very unfortunate "features".
chr(n) throws various runtime warnings where 'n' isn't kosher UCS, and
"\x{h...h}" throws the same ones at compile time.
(...)I'm not sure I see the point of picking on a few values to warn
about.
I don't see the point, but Perl's warnings are arbitrary in several
ways. Abigail has a lightning talk about the "interpreted as function"
warning, that illustrates this.
OK. In the meantime IMHO chr(n) should be handling utf8 and has no
business worrying about things which UTF-8 or UCS think aren't
characters.
Note that chr(n) is whingeing about 0xFFFE, which Encode::en/decode
(UTF-8) are happy with. Unicode defines 0xFFFE and 0xFFFF as
non-characters, not just 0xFFFF (which Encode::en/decode do deem
invalid).
In any case, is chr(n) supposed to be utf8 or UTF-8 ? AFAIKS, it's
neither.
It's supposed to be neither on the outside. Internally, it's utf8.
One can turn off the warnings and then chr(n) will happily take any +ve
integer and give you the equivalent character -- so the result is utf8,
but the warnings are some (very) small subset of checking for UTF-8 :-(
I wonder what happens for n >= 2^64. The encoding runs out at 2^72 !
If chr(-1) doesn't exist, then undef looks like a reasonable
return value -- returning "\x{FFFD}" makes chr(-1)
indistinguishable from chr(0xFFFD) -- where the first is
nonsense and the second is entirely proper.
0xFFFD is the Unicode equivalent of undef. I think it makse sense in
this case.
Well...
Unicode says: "REPLACEMENT CHARACTER: used to represent an incoming
character whose value is unknown or unrepresentable in Unicode".
...so it has plenty to do without being used to represent a value which
is completely beyond the range for characters, and for which perl has a
perfectly good convention already.
...besides, if I want to see if chr(n) has worked I have to check that
(a) the result is not "\xFFFD" and (b) that n is not 0xFFFD.
So we'll have to differ on this :-)
Chris
--
Chris Hall highwayman.com +44 7970 277 383
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