You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: argument_splitter.rs
    path of file: ./repos/parallel/src/execute
    
    the code of the file until where you have to start completion: const DOUBLE: u8 = 1;
const SINGLE: u8 = 2;
const BACK:   u8 = 4;
const COMM_1: u8 = 8;
const COMM_2: u8 = 16;
const VARIAB: u8 = 32;
const ARRAY:  u8 = 64;
const METHOD: u8 = 128;

/
    
    fn next(&mut self) -> Option<&'a str> {
        while let Some(&b' ') = self.data.as_bytes().get(self.read) {
            self.read += 1;
        }
        let start = self.read;

        let (mut level, mut array_level, mut array_process_level) = (0, 0, 0);
        for character in self.data.bytes().skip(self.read) {
            match character {
                _ if self.flags & BACK != 0 => self.flags ^= BACK,
                b'\\'                       => self.flags ^= BACK,
                b'@' if self.flags & SINGLE == 0 => {
                    self.flags &= 255 ^ COMM_1;
                    self.flags |= COMM_2 + ARRAY;
                    self.read += 1;
                    continue
                },
                b'$' if self.flags & SINGLE == 0 => {
                    self.flags &= 255 ^ COMM_2;
                    self.flags |= COMM_1 + VARIAB;
                    self.read += 1;
                    continue
                },
                b'['  if self.flags & SINGLE == 0 && self.flags & COMM_2 != 0 => array_process_level += 1,
                b'['  if self.flags & SINGLE == 0 => array_level += 1,
                b']'  if self.flags & SINGLE == 0 && array_level != 0 => array_level -= 1,
                b']'  if self.flags & SINGLE == 0 => array_process_level -= 1,
                b'('  if self.flags & SINGLE == 0 && self.flags & COMM_1 != 0 => level += 1,
                b'('  if self.flags & SINGLE == 0 && self.flags & (VARIAB + ARRAY) != 0 => {
                    self.flags |= METHOD;
                    self.flags &= 255 ^ (VARIAB + ARRAY);
                },
                b')'  if self.flags & SINGLE == 0 && self.flags & METHOD != 0 => {
                    self.flags &= 255 ^ METHOD;
                },
                b')'  if self.flags & SINGLE == 0 => level -= 1,
                b'"'  if self.flags & SINGLE == 0 => self.flags ^= DOUBLE,
                b'\'' if self.flags & DOUBLE == 0 => self.flags ^= SINGLE,
                b' '  if self.flags & (SINGLE + DOUBLE + METHOD) == 0
                    && level == 0 && array_level == 0 && array_process_level == 0 => break,
                _ => ()
            }
            self.read += 1;
            self.flags &= 255 ^ (COMM_1 + COMM_2);
        }

        if start == self.read {
            None
        } else {
            Some(&self.data[start..self.read])
        }
    }