Dear monks,

using the following code

print "- " =~ /\s*\p{Dash}\s*/;    # 1
print "- " =~ /\s*\p{Dash}{1}\s*/; # 2
print "- " =~ /\s*-\s*/;           # 3

[download]
only line 2 and 3 matches. Debugging the regex makes clear why: 
Compiling REx "\s*\p{Dash}\s*"
synthetic stclass "ANYOF[\11\12\14\15 ][{unicode_all}+utf8::Dash]".
Final program:
   1: STAR (3)
   2:   SPACE (0)
   3: ANYOF[{unicode}+utf8::Dash] (15)
  15: STAR (17)
  16:   SPACE (0)
  17: END (0)
stclass ANYOF[\11\12\14\15 ][{unicode_all}+utf8::Dash] minlen 1 
Matching REx "\s*\p{Dash}\s*" against "- "
Matching stclass ANYOF[\11\12\14\15 ][{unicode_all}+utf8::Dash] agains
+t "- " (2 chars)
   1 <-> < >                 |  1:STAR(3)
                                  SPACE can match 1 times out of 21474
+83647...
   2 <- > <>                 |  3:  ANYOF[{unicode}+utf8::Dash](15)
                                    failed...
   1 <-> < >                 |  3:  ANYOF[{unicode}\-...+utf8::Dash](1
+5)
                                    failed...
                                  failed...
Contradicts stclass... [regexec_flags]
Match failed
Freeing REx: "\s*\p{Dash}\s*"

[download]

The first \s* matches the second character of "- " and the \p{Dash} fails, since the regex does not backtrack beyond the last space. But shouldn't there be a match?

Version 3 obviously matches because of some optimization (seraching for "-"), but why does Version 2 match, since it should be equivalent to 1?

Is this a bug or does my first regex simply not do what I think?

Cheers, Andrew

In reply to Strange re behaviour for /\s*\p{Dash}\s*/ - bug or feature? by Anonymous Monk

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