regex - Efficiency of lookarounds in C# regular expressions. Should I avoid them if I can? -

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everyone! i'm quite new regular expressions, them, lot!

call me nitpicky if will, i'd know if should avoid using lookaheads , lookbehinds if have option.

for example, 2 commands below same thing, 1 uses lookbehind , other doesn't.

the_str = regex.replace(the_str, @"(;|!|\?) \.{3}", "$1...");  the_str = regex.replace(the_str, @"(?<=(;|!|\?)) \.{3}", "...");

which 1 use? more efficient?

thanks answers!

i tested both locally , method using lookbehind 25% slower.

another variation tested using lookahead instead of lookbehind 10% slower:

s = regex.replace(s, @"(;|!|\?) (?=\.{3})", "$1");

i don't think there's enough of performance difference advise avoiding lookarounds. if think makes code more readable use them. optimize performance if profiling shows have performance problem , regular expression bottleneck.

for information, string tested on "blah; ... foo ...; bar bar ? ..." repeated 1000 times , repeated each test 100 times.

 0.944s   no lookarounds    regex.replace(s, @"(;|!|\?) \.{3}", "$1...")  1.027s   ahead        regex.replace(s, @"(;|!|\?) (?=\.{3})", "$1") 1.210s   behind       regex.replace(s, @"(?<=(;|!|\?)) \.{3}", "...") 1.124s   both              regex.replace(s, @"(?<=(;|!|\?)) (?=\.{3})", "")

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