in reply to Re^4: about style: use possessive or atomic?
in thread about style: use possessive or atomic?

Is it true that ($match){1}+ equals to simply $match? Yes, and the + does nothing here, as you can see with use warnings:

That's only true because you the OP included a quantifier in the embedded regex; and you get 3 fails because your anchors guarantee the regex used couldn't succeed (which doesn't seem like a useful test?)

This shows that {n}+ is a valid quantifier:

use strict;
use warnings;

chomp(my $match = <DATA>);
chomp(   $_     = <DATA>);

for my $regex (
                  "($match){1}+",
                  "($match){1}",
                  "($match)",
                  "($match)+",
                  "($match)+?",
              )
{
    print qw(FAIL SUCCESS)[ !! m/$regex/ ], "\n"
}

__DATA__
(?:a|b)
bbab

[download]
C:\test>junk37
SUCCESS
SUCCESS
SUCCESS
SUCCESS
SUCCESS

[download]
With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
"Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
In the absence of evidence, opinion is indistinguishable from prejudice.
I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!

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Re^6: about style: use possessive or atomic?
by Athanasius (Archbishop) on Aug 16, 2015 at 13:25 UTC

    Hello BrowserUk,

    I still get the warning when the regex isn’t embedded:

    23:15 >perl -wE "my $r = qr{(?:a|b)}; say $r;"
(?^u:(?:a|b))

23:17 >perl -wE "my $r = qr{(?:a|b){1}}; say $r;"
(?^u:(?:a|b){1})

23:17 >perl -wE "my $r = qr{(?:a|b){1}+}; say $r;"
Useless use of greediness modifier '+' in regex; marked by <-- HERE in
+ m/(?:a|b){1}+ <-- HERE / at -e line 1.
(?^u:(?:a|b){1}+)

23:17 >perl -v

This is perl 5, version 22, subversion 0 (v5.22.0) built for MSWin32-x
+64-multi-thread
...

    [download]

    I get the same warning with Strawberry Perl v5.20.2, but not with v5.18.2. Is the warning erroneous?

    Athanasius <°(((>< contra mundum Iustus alius egestas vitae, eros Piratica,

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[d/l]
      I get the same warning with Strawberry Perl v5.20.2, but not on v5.18.2.

      You're right! My default perl is currently 5.18:

      C:\test>\perl5.18\perl\bin\perl.exe junk37.pl
SUCCESS
SUCCESS
SUCCESS
SUCCESS
SUCCESS

C:\test>\Perl5.20\bin\perl.exe junk37.pl
Useless use of greediness modifier '+' in regex; marked by <-- HERE in
+ m/((?:a|b)){1}+ <-- HERE / at junk37.pl line 15, <DATA> line 2.
SUCCESS
SUCCESS
SUCCESS
SUCCESS
SUCCESS

C:\test>\Perl22\bin\perl.exe junk37.pl
Useless use of greediness modifier '+' in regex; marked by <-- HERE in
+ m/((?:a|b)){1}+ <-- HERE / at junk37.pl line 15, <DATA> line 2.
SUCCESS
SUCCESS
SUCCESS
SUCCESS
SUCCESS

      [download]
      Is the warning erroneous?

      Erm. I was relying on Perl to tell me :)

      The fact that the warning has been recently added suggests it is probably correct.

      That said, the construct is still listed in the 5.22 docs:  {n}+   Match exactly n times and give nothing back (redundant); which basically means your guess is as good as anybody's at this point?

      With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'
      Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.
      "Science is about questioning the status quo. Questioning authority". I knew I was on the right track :)
      In the absence of evidence, opinion is indistinguishable from prejudice.
      I'm with torvalds on this Agile (and TDD) debunked I told'em LLVM was the way to go. But did they listen!
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      > Is the warning erroneous?

      if the meaning of {n}+ hasn't be deprecated or changed its a totally wrong warning.

      Please run my code with 5.20, with same results we should file a bug report.

      edit

      As you can see there its not redundant.

      The plus is neither a greedyness operator here, bc its in second place, its there to stop backtracking.

      update
      Apparently adding the second + turns the whole quantifier {n}+ into a possessive quantifier.

      see here

      Like a greedy quantifier, a possessive quantifier repeats the token as many times as possible. Unlike a greedy quantifier, it does not give up matches as the engine backtracks. With a possessive quantifier, the deal is all or nothing. You can make a quantifier possessive by placing an extra + after it. * is greedy, *? is lazy, and *+ is possessive. ++, ?+ and {n,m}+ are all possessive as well.

      so + is "greedy" and ++ "possessive", {n}+ is analogous to ++ .

      Cheers Rolf
      (addicted to the Perl Programming Language and ☆☆☆☆ :)
      Je suis Charlie!

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        so I installed 5.20.2 via perlbrew and it's even getting scarier, the behaviour of {n}+ has changed.

          DB<3> print "aaa" =~ /(a+){1}+a/
aa
  DB<4> print "aaa" =~ /(a+){1}a/     
aa
  DB<5> print $]
5.020002

        [download]

        while with 5.14 it's still like documented:

          DB<1> print "aaa" =~ /(a+){1}+a/

  DB<2> print "aaa" =~ /(a+){1}a/
aa
  DB<3> print $]
5.014002

        [download]

        This is worse than an erroneous warning that's a fatal break of backwards compatibility!

        update

        5.20 is backtracking while told otherwise

        Read more... (2 kB)

        And that's the trace from 5.14

        Read more... (4 kB)

        Cheers Rolf
        (addicted to the Perl Programming Language and ☆☆☆☆ :)
        Je suis Charlie!

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