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Postings from August 2001
"Jeff 'japhy/Marillion' Pinyan" <jeffp@crusoe.net> wrote:
:This is forwarded from a conversation I had with Jeff Friedl.
:
:==========================================================================
:Jeff 'japhy/Marillion' Pinyan <jeffp@crusoe.net> wrote:
:
:|> The only problem is (understandable) that $&, while updated in a
:|> look-ahead, is NOT "down"dated in a look-behind:
:|>
:|> "japhy" =~ m{
:|> ..
:|> (?{ print "<$`><$&><$'>" })
:|> (?=
:|> ..
:|> (?{ print "<$`><$&><$'>" })
:|> )
:|> (?<=
:|> ..
:|> (?{ print "<$`><$&><$'>" })
:|> )
:|> (?{ print "<$`><$&><$'>" })
:|> }x;
:|>
:|> The output is:
:|>
:|> <><ja><phy>
:|> <><japh><y>
:|> <><ja><phy>
:|> <><ja><phy>
:
:The 2nd one looks like a bug to me. The lookahead is just that, lookahead,
:and so I feel that it should never (ever) be part of $&. The other ones
:seem as I would expect them.
If you change the lookbehind to this:
(?<=
(?{ print "<$`><$&><$'>" })
..
)
you get:
<><ja><phy>
<><japh><y>
<><><japhy>
<><ja><phy>
.. which makes slightly more sense.
We don't currently sign any contract to guarantee the value of $& and
friends inside a regexp. I'm not convinced that we ought to - if you
choose to document this, I'd strongly recommend a warning that it may
change in the future.
Hugo
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