Maurice Height wrote:
> I have just solved a bug in my code involving a compiled regex.
> I am wondering if I have got it wrong or if this is a Perl error.
> To explain...
>
> I had a class ABC in which I passed a value to the constructor
> (eg: $arg{delim_str} ) and stored this for later use throughout the class:
>
> $self->{DELIM_RE} = qr/\Q$arg{delim_str}\E/os;
>
> Now when I create 2 class objects, each with a different value of
> $arg{delim_str}, the first instance works correctly, but the second
> seems to be using the same value that was created in the first instance.
To my understanding, that's what it's supposed to do. The /o says
you don't have to re-interpolate the contents of $arg{delim_str}
after the first time. So just remove the /o and you should be fine.
> For example:
>
> my $abc1 = ABC->new( delim_str => q{|} );
> # do some stuff with $abc1
> ....
>
> my $abc2 = ABC->new( delim_str => q{,} );
> # do some stuff with $abc2
> *** does not work because the value of $self->{DELIM_RE}
> *** used in $abc2 is the same as that in $abc1
>
> However if I remove the 'o' option from the regex, everything is OK.
>
> $self->{DELIM_RE} = qr/\Q$arg{delim_str}\E/s;
>
> I had assumed that even though a regex is compiled once only with the 'o'
> option, that instances of class data would be INDEPENDENT of each other.
Apparently not a good assumption.
perlretut man page:
Part 1: The basics
...
Using regular expressions in Perl
...
There are a few more things you might want to know about matching operators.
First, we pointed out earlier that variables in regexps are substituted
before the regexp is evaluated:
$pattern = 'Seuss';
while (<>) {
print if /$pattern/;
}
This will print any lines containing the word "Seuss". It is not as
efficient as it could be, however, because perl has to re-evaluate $pattern
each time through the loop. If $pattern won't be changing over the lifetime
of the script, we can add the "//o" modifier, which directs perl to only
perform variable substitutions once:
#!/usr/bin/perl
# Improved simple_grep
$regexp = shift;
while (<>) {
print if /$regexp/o; # a good deal faster
}
_______________________________________________
Perl-Win32-Users mailing list
Perl-Win32-Users@listserv.ActiveState.com
To unsubscribe: http://listserv.ActiveState.com/mailman/mysubs
