in reply to Re^5: about style: use possessive or atomic?
in thread about style: use possessive or atomic?

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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Re^7: about style: use possessive or atomic?
by BrowserUk (Patriarch) on Aug 16, 2015 at 13:41 UTC
    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'
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        That absolutely makes sense, and I like when warnings like this get added. Any time someone can be warned whenever they are trying to use something useless is another tool that will potentially help someone who's trying to debug something they don't understand: "I'm using a quantifier, but why the heck isn't it working!".

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Re^7: about style: use possessive or atomic? (bug)
by LanX (Saint) on Aug 16, 2015 at 20:18 UTC
    > 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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        So I think that you can post it to perlbug with a link to this node?
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