comments and qw

Tanktalus has asked for the wisdom of the Perl Monks concerning the following question:

I find myself doing this a fair bit (though with significantly longer lists - anywhere from 2 to 20 entries, depending):

do_something($_) for qw(
  foo
  bar
  baz
  );
[download]

It allows me to trivially add something or remove something. Well, removing isn't quite as nice as with regular lists - I can't just comment it out, I have to delete the whole line. However, what I can't do with this is do something like:

do_something($_) for qw(
  foo
  bar  # introduced November, 2005
  baz  # deprecated - remove by December, 2006
  );
[download]

(This does actually tell me it can't do it with a warning message: Possible attempt to put comments in qw() list at ./x.pl line 10.) The closest I can come up with is something like this:

#!/usr/bin/perl

use strict;
use warnings;

do_something($_) for qw(
  foo
  bar  # introduced November, 2005
  baz  # deprecated - remove by December, 2006
  );

print "-----------------\n";

do_something($_) for words( <<WORDS );
  foo
  bar  # introduced November, 2005
  baz  # deprecated - remove by December, 2006
WORDS


sub do_something
{
    print " [$_[0]]\n";
}

sub words
{
    my @lines = split /\n/, shift;
    s/#.*$// for @lines;
    map { split ' ', $_ } @lines;
}
[download]

However, I'm pretty sure that it's way slower than any solution that allows the perl parser to do it. And, for some reason, it just doesn't feel elegant. And, for that reason, I haven't actually gone there - I'm not currently inserting comments into my lists.

Has anyone ever had a similar desire? What solution did you use?

Comment on comments and qw Select or Download Code

Replies are listed 'Best First'.
Re: comments and qw by brian_d_foy (Abbot) on Feb 12, 2006 at 17:12 UTC
Sure I've had a similar desire, but since Perl doesn't allow us to do what you want to do, I don't do that. :) If I really want to comment a list, I don't use qw(). Anything else that I might do is just added complexity that I don't need and will probably confuse later programmers. `do_something($_) for ( 'foo', 'bar', # introduced November, 2005 'baz', # deprecated - remove by December, 2006 );` [download] -- brian d foy <brian@stonehenge.com> Subscribe to The Perl Review	[reply] [d/l]
Re: comments and qw by rnahi (Curate) on Feb 12, 2006 at 18:33 UTC
It should not be to hard to implement, since there is a similar mechanism to allow comments in regular expressions with the /x modifier. Here is a quick example of a qwx function. `#!/usr/bin/perl use strict; use warnings; use Data::Dumper; sub qwx { my ( $text ) = @_; $text =~ s/\s[#].$//mg; return split ' ', $text; } my @items = qwx( ' this is # possibly a # commented list ' ); print Dumper \@items; __END__ $VAR1 = [ 'this', 'is', 'a', 'list' ];` [download]	[reply] [d/l]
Re^2: comments and qw by ikegami (Patriarch) on Feb 12, 2006 at 19:10 UTC
It might be useful to skip blank lines (or lines that just contain comments) like the real `qw()`: `sub qwx { local $_ = @_ ? $_[0] : $_; s/[#].*$//mg; s/^\s+//; s/\s+$//; s/\s+/ /g; return split ' ', $text; }` [download] Also, you could tweak the appearance of caller a little as follows: `my @items = qwx" this is # possibly a # commented list ";` [download] Single quote won't work without a space before it.	[reply] [d/l] [select]
Re^3: comments and qw by rnahi (Curate) on Feb 12, 2006 at 20:32 UTC
It might be useful to skip blank lines (or lines that just contain comments) like the real qw(): That won't be necessary. split with a single space is a special case that splits on any number of whitespace, including newlines. Try it for yourself: `#!/usr/bin/perl use strict; use warnings; use Data::Dumper; sub qwx { my ( $text ) = @_; $text =~ s/\s[#].$//mg; return split ' ', $text; } my @items = qwx" this is # possibly a # commented list # with stand-alone comments # and empty lines " ; print Dumper \@items; __END__ $VAR1 = [ 'this', 'is', 'a', 'list' ];` [download]	[reply] [d/l]
Re^4: comments and qw by ikegami (Patriarch) on Feb 13, 2006 at 03:08 UTC
Re: comments and qw by Fletch (Bishop) on Feb 12, 2006 at 18:17 UTC
Would Re: Build your array with push (and the other responses to the parent Build your array with push) be applicable? (As for speed I'm pretty sure YAML::Syck would be fairly quick)	[reply]
Re: comments and qw by bsb (Priest) on Feb 13, 2006 at 09:47 UTC
You could play bareword roulette: `use strict; no strict 'subs'; do_something($_) for ( foo, # comment bar, baz, );` [download]	[reply] [d/l]
Re^2: comments and qw by Roy Johnson (Monsignor) on Feb 13, 2006 at 15:44 UTC
You could also use `=>` to effectively `qw` all the list members. (I use keywords here to show that there's no roulette being played. They're interpreted as strings.) `do_something($_) for ( exit => # comment sub => exec => do_something => # It's a string here, not a sub call! ); sub do_something { print "Got ($_[0])\n"; }` [download] Keep in mind that `qw` and `=>` have somewhat different rules about what they quote: `qw` effectively quotes each run of non-whitespace; `=>` quotes only runs of "word" (alpha-num-underscore) characters, and interprets everything else. Caution: Contents may have been coded under pressure.	[reply] [d/l] [select]
Re: comments and qw by stefp (Vicar) on Feb 26, 2006 at 04:01 UTC
TimToady had not seen this thread otherwise he would have advertised that was a no-brainer in Perl6. I asked him but could not find that thread again. Hopefully I crossed again it in "best nodes" So from the mouth of the horse^Wcamel and some other #perl6 usual suspects: Feb 23 00:05:33 <cognominal> recently in perlmonks someone wanted a + qw() that supported comments, is there an idiom for that in perl6? Feb 23 00:06:02 <Juerd> cognominal: <<>>, IIRC Feb 23 00:06:43 <cognominal> I was surprised not to see TimToady pu +shing a Perl6 solution :) Feb 23 00:07:10 <TimToady> cognominal: I don't think we actually sa +id anything about comments, but considering that it's "shell quoting" +, and shells have comments, they could sneak in there... Feb 23 00:07:12 <Juerd> It could still happen Feb 23 00:07:45 <Juerd> TimToady: But let's not have \\\n :) Feb 23 00:07:55 <TimToady> Didn't see that PM thread... Feb 23 00:08:03 <audreyt> shells have line-terminated comments Feb 23 00:08:13 <Juerd> audreyt: That was implied :) Feb 23 00:08:21 <TimToady> So put line breaks in. Feb 23 00:08:36 * audreyt purrs randomly Feb 23 00:09:51 <audreyt> my @x = << Feb 23 00:09:59 <audreyt> This is some splitted words # but not + this Feb 23 00:10:05 <audreyt> and this too # but not this Feb 23 00:10:07 <audreyt> >>; [download] -- stefp	[reply] [d/l]