Re: Variable character class

[Gianni Ceccarelli]

On Wed, 4 Sep 2019 21:44:29 -0700
William Michels via perl6-users <perl6-users@perl.org> wrote:

> Hi Gianni, I'm not sure of the Perl5 case, but what you're saying is,
> if your target string is backslashed, be sure to "quote-interpolate
> it" in Perl6? (see below):

Re-reading what I wrote, I realise it was really not clear. Let me try
again.

yary's original code was::

  sub matching_chars {
    (my $chars_to_match, local $_) = @_;
    /([$chars_to_match]+)/
  }
  say matching_chars('+\/\]\[', 'Apple ][+//e'); # says ][+//

If ``matching_chars`` took "a set of characters expressed as a string"
as its first argument, you'd expect to be able to say::

  say matching_chars('+/][', 'Apple ][+//e');

but this doesn't work, because it tells Perl5 to compile this regex::

  ([+/][])+

which doesn't compile ("Unmatched [ in regex").

Sidhekin's Perl6 version doesn't have this issue. On the other hand,
this happens::

  sub matching_chars(Str $chars_to_match, Str $target) {
    my @chars-to-match = $chars_to_match.comb;
    return $target ~~ m:g/@chars-to-match + /;
  }

  is matching_chars('+/][', Q{Apple ][+//\\e}),['][+//'];
  is matching_chars('+\/][', Q{Apple ][+//\\e}),[Q{][+//\\}];


The "fixed" Perl5 version would be::

  /([\Q$chars_to_match\E]+)/

or, equivalently::

  $chars_to_match = quotemeta($chars_to_match);
  /([$chars_to_match]+)/

Does that help?

-- 
        Dakkar - <Mobilis in mobile>
        GPG public key fingerprint = A071 E618 DD2C 5901 9574
                                     6FE2 40EA 9883 7519 3F88
                            key id = 0x75193F88

You have literary talent that you should take pains to develop.