split a string by length like str_split() from php ported to lua

str_split.lua

--
-- based on https://www.php.net/manual/en/function.str-split.php
-- feel to free to validate/adjust to uses asserto/error
--
-- Denis Dos Santos Silva
--

local function str_split(str, length)
    local result = {}
    local index = 1

    if (type(str) ~= 'string') then return result; end

    if (not length) then length=1; end
    if (length <= 0) then return result; end
    if (length > slen) then return result; end

    local slen = #str;
    while index <= slen do
        table.insert(result, string.sub(str, index, index + length - 1))
        index = index + length
    end

    return result
end

return str_split

test.lua

local str_split = require 'str_split'
local s = 'hello world'

for i=1, #s do
print( table.concat(str_split(s, i), '-') )
end

print( table.concat(str_split(s), '-') )
print( table.concat(str_split(s, #s), '-') )
print( table.concat(str_split(s, #s+1), '-') )
print( table.concat(str_split(s, 0), '-') )