Re: the most optimal string "trim" implementation

[David Manura <dm.lua@...>]

On Fri, Dec 25, 2009 at 12:25 AM, David Manura wrote:
> I contend [1] that the most optimal way to implement a string "trim"
> function is basically this:
>  function trim(s) return s:match'^%s*(.*%S)%s*$' or '' end
On Sat, Dec 26, 2009 at 1:03 AM, David Manura wrote:
> On Fri, Dec 25, 2009 at 6:22 AM, Shmuel Zeigerman wrote:
>>  function trim(s) return s:match'^%s*(.*%S)' or '' end
> Yes, that is even better.

I'll have to retract this conclusion.  The implementation performs
very well except in the case of a long string with only whitespace, in
which case it performs very poorly.  In the latter condition the
pattern finds no match, and the juxtaposition of "%s*" with ".*"
causes substantial backtracking (see recent "Pattern matching: good
practices ?" thread).  So, I fall back to the following as the most
optimal known implementation:

  local match = string.match
  function trim(s)
    return match(s,'^%s*$') and '' or match(s,'^%s*(.*%S)')
  end