Using positive-lookahead (?=regex) with re2

regex go re2
a8m picture a8m · May 18, 2015 · Viewed 12.9k times · Source

Since I'm a bit new with re2, I'm trying to figure out how to use positive-lookahead (?=regex) like JS, C++ or any PCRE style in Go.

Here's some examples of what I'm looking for.

JS:

'foo bar baz'.match(/^[\s\S]+?(?=baz|$)/);

Python:

re.match('^[\s\S]+?(?=baz|$)', 'foo bar baz')
  • Note: both examples match 'foo bar '

Thanks a lot.

Answer

Kobi picture Kobi · May 18, 2015

According to the Syntax Documentation, this feature isn't supported:

(?=re) before text matching re (NOT SUPPORTED)

Also, from WhyRE2:

As a matter of principle, RE2 does not support constructs for which only backtracking solutions are known to exist. Thus, backreferences and look-around assertions are not supported.

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