Bench mark of tolower(), split() and map() in VimL

map_time.vim

let pathext = ".COM;.EXE;.BAT;.CMD;.VBS;.VBE;.JS;.JSE;.WSF;.WSH;.MSC;.PY;.tcl"
let s:path_separator = ";"

" Time of split
let stime = reltime()
for i in range(1, 1000)
  let s:path_extensions = split(tolower(pathext), s:path_separator)
endfor
echo reltimestr(reltime(stime)) . " (split) " . len(s:path_extensions)
echo s:path_extensions
unlet s:path_extensions

" Time of split + map
let stime = reltime()
for i in range(1, 1000)
  let s:path_extensions = map(split(pathext, s:path_separator), 'tolower(v:val)')
endfor
echo reltimestr(reltime(stime)) . " (split + map) " . len(s:path_extensions)
echo s:path_extensions
unlet s:path_extensions

Result:

  0.009567 (split) 13
['.com', '.exe', '.bat', '.cmd', '.vbs', '.vbe', '.js', '.jse', '.wsf', '.wsh',
'.msc', '.py', '.tcl']
  0.197191 (split + map) 13
['.com', '.exe', '.bat', '.cmd', '.vbs', '.vbe', '.js', '.jse', '.wsf', '.wsh',
'.msc', '.py', '.tcl']

Using map() is 20 times slower.