bad argument when using localize ngx.re.find

[zcong]

openresty-1.13.6.2
I wrote function like this

function _M.find_in_string(source_string, matching_string)
    return ngx.re.find(source_string, matching_string, "jo")
end

and I try to replace the ngx.re.find with localize var like this

local ngx_re = ngx.re
local ngx_re_find = ngx_re.find
function _M.find_in_string(source_string, matching_string)
    return ngx_re_find(source_string, matching_string, "jo")
end

the first version find_in_string(nil, "") will return nil
the second version find_in_string(nil, "") will raise an exception: bad argument #1 to 'find_in_string' (string expected, got nil)

why is that?

[cuiweixie]

the second version call the old lua-c version ngx.re.find, and the first version call the ffi base (after requre "resty.core") version will cause this. by the way the newest version of openresty load the ffi function at lua vm init.

[thibaultcha]

Considering this answered. Thanks for the help @cuiweixie.

[jils2013]

should we remove localize for ngx.re.find?

the second version call the old lua-c version ngx.re.find, and the first version call the ffi base (after requre "resty.core") version will cause this. by the way the newest version of openresty load the ffi function at lua vm init.