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Am 03.11.2014 um 09:32 schröbte Marco Mastropaolo:
If I remember correctly, the first thing gsub does is checking if the
second argument is a pattern or not and, if not, it goes on with a direct
replace. Thus the performance impact is minimal in that case -a linear scan
over the second arg string.
AFAICS, only `string.find` does that (if the `plain` argument is falsish).
This if I understood the question correctly, if not, sorry :)
Il 03/nov/2014 06:09 "Rv Rv" <rvrv7575@yahoo.com> ha scritto:
The Lua API string.gsub will also take a pattern as an argument. I am
assuming that because of the assumption that a pattern may be present as an
argument, there will be additional processing that will be done every time
a string comparison is made. If we know for sure that the argument is
going to be a string, is there way to avoid this additional performance
penalty. I was looking for an API that operates only on string like strcpy
in C , but could not find anything
Is there any faster way to do string substitution in Lua apart from using
string.gsub.
There has been a discussion about a similar `plain` option for `string.gsub` not long ago[1]. You could implement something like that in C quite easily (using Lua's `luaL_Buffer` API), but AFAIK noone has done so yet. You can try one of the real regex libraries[2] for Lua -- a regular _expression_ compiled to a finite state machine could be faster than an interpreted Lua pattern. And of course it's always worth checking out LPeg[3] (although I doubt that it will be faster in this case).
Always assuming that string substitution is actually a bottleneck in your program ...
Philipp
[1]: http://lua-users.org/lists/lua-l/2014-08/msg00584.html
[2]: http://rrthomas.github.io/lrexlib/
[3]: http://www.inf.puc-rio.br/~roberto/lpeg/lpeg.html