Hello,
This is definitely an edge case, but an interesting one. Suppose we
have a configuration string like “mux:off mix:on” and we want to match
the “mix:on” (actually either) part passively (i.e. not captured).
“mux:on mix:off” =~ /\b(?mix:(on|off))\b/
=> 4
Oops, forgot about options. 100% understandable.
Several attempts to work around it
Wrap one of the option characters in a set
“mux:on mix:off” =~ /\b(?[m]ix:(on|off))\b/
SyntaxError: (irb):2: undefined group option: /\b(?[m]ix:(on|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in
`’
Wrap all option characters in individual sets
“mux:on mix:off” =~ /\b(?[m][i][x]:(on|off))\b/
SyntaxError: (irb):3: undefined group option:
/\b(?[m][i][x]:(on|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in
`’
Wrap the option characters in a group
“mux:on mix:off” =~ /\b(?(mix):(on|off))\b/
SyntaxError: (irb):4: undefined group option: /\b(?(mix):(on|off))\b/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in
`’
Move the anchors inside the passive group
“mux:on mix:off” =~ /(?\b(([m]ix):(on|off))\b)/
SyntaxError: (irb):5: undefined group option:
/(?\b(([m]ix):(on|off))\b)/
from /Users/ammar/.rvm/rubies/ruby-1.9.2-p0/bin/irb:17:in
`’
If the passivity is dropped, it works as intended, of course.
“mux:on mix:off” =~ /\b(mix:(on|off))\b/
=> 7
The same occurs with ruby 1.8, but with a slightly different error
message:
undefined (?..) sequence:
I was hoping that one of the workarounds above would work, but now I’m
thinking this is might be a bug. I want to see what others think
before I cry wolf.
Regards,
Ammar