Porters,
One of my blog friend came across with this. When you feed perl a
bogus unicode property, it raises an exception like 'Can't find
Unicode property definition "Bogus" at uniprop.pl line 17.
'. But this does not always work. Here is a sample code.
#!/usr/local/bin/perl
my $count = 0;
sub p { print $count++, " : ", (map {s/\n//g; $_ } @_), "\n" } # 4
convenience;
p eval{ "" =~ /\p{IsBogus}/ }, $@; # no exception
p eval{ "str" =~ /\p{IsBogus}/ }, $@; # exception
p eval{ "str" =~ /^\p{IsBogus}/ }, $@; # exception
p eval{ "str" =~ /\p{IsBogus}$/ }, $@; # exception
p eval{ "str" =~ /\A\p{IsBogus}/ }, $@; # exception
p eval{ "str" =~ /\p{IsBogus}\Z/ }, $@; # exception
p eval{ "str" =~ /\b\p{IsBogus}/ }, $@; # exception
p eval{ "str" =~ /\w\p{IsBogus}/ }, $@; # exception
p eval{ "str" =~ /A\p{IsBogus}/ }, $@; # no exception
p eval{ "str" =~ /[A-Z]\p{IsBogus}/ }, $@; # no exception
__END__
Seems like any flavor of perl 5.8 and above behave that way.
I have told my friend to use a small code like this to tell if the
property name exists but that's an ad-hoc solution.
sub has_unicode_property{
my $prop = shift;
my $re = qr/\p{$prop}/;
eval { 'string' =~ $re }; # must match against non-empty string
return $@ ? 0 : 1;
}
I have checked the code and it's done at utf8.c (Perl_swash_init())
and lib/utf8_heavy.pl but that's how far I could go in 1/4 hours or so.
Dan the Perl5 Porter
