From: matt@... (matt neuburg)
Date: 2008-04-12T01:20:24+09:00
Subject: surprise in sub

irb(main):001:0> s = "\\\\"
=> "\\\\"
irb(main):002:0> s.length
=> 2
irb(main):003:0> s = "howdy".sub("howdy", s)
=> "\\"
irb(main):004:0> s.length
=> 1

So merely using a string as the second param of sub (the replacement
value) can cause that string to be altered.

Now, the documentation does "warn" that sequences \1, \2 etc. are valid
in the replacement string. This suggests that the replacement string is
processed before use; to be sure, it says nothing about "\\" explicitly,
but I do see of course that one must deal with "\\" in order to escape
the escaping. Furthermore, there's a "workaround", namely to write the
third line as follows:

s = "howdy".sub("howdy") {|x| s}

Still, I got seriously caught by this behavior and it was tricky to
track down. m.

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