slicejson 0.1.2

parse json through string slice,try to make it faster!
Documentation 
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use std::{iter::Peekable, str::CharIndices};

#[derive(Debug)]
pub struct CharPos {
    pub ch: char,
    pub offset: usize,
}

#[derive(Debug, Default, Clone, PartialEq, Eq, Hash)]
pub struct PosRange {
    pub start: usize,
    pub end: usize, //inclusive
}
impl PosRange {
    pub fn new(start: usize, end: usize) -> Self {
        PosRange { start, end }
    }
}

#[derive(Debug)]
pub struct Tokenizer<'input> {
    pub s: &'input str,
    pub peek: Peekable<CharIndices<'input>>,
    pub ch: Option<CharPos>,
    bak_ch: Option<CharPos>,
    pub str_token: Vec<usize>,
}

impl<'input> Tokenizer<'input> {
    pub fn new(input: &'input str) -> Tokenizer<'input> {
        let peek = input.char_indices().peekable();
        // let next = peek.next().unwrap();
        // let ch = Some(CharPos { ch: next.1, offset: next.0 });
        Self {
            s: input,
            peek,
            ch: None,
            bak_ch: None,
            str_token: vec![],
        }
    }

    pub fn get_char(&mut self) {
        if self.bak_ch.is_some() {
            self.ch = self.bak_ch.take();
            return;
        }
        let next = self.peek.next();
        match next {
            None => self.ch = None,
            Some((offset, ch)) => {
                if self.ch.is_none() {
                    self.ch = Some(CharPos { ch, offset });
                } else {
                    self.ch.as_mut().unwrap().ch = ch;
                    self.ch.as_mut().unwrap().offset = offset;
                }
            }
        }
    }

    pub fn peek(&mut self) -> Option<CharPos> {
        let cur = self.peek.peek();
        match cur {
            None => None,
            Some((offset, ch)) => Some(CharPos {
                ch: *ch,
                offset: *offset,
            }),
        }
    }

    pub fn concat(&mut self) {
        let ch = self.ch.take();
        self.str_token.push(ch.unwrap().offset);
    }

    pub fn get_str_token(&mut self) -> PosRange {
        let start = self.str_token.first().map_or(0 as usize, |v| *v);
        let end = self.str_token.last().map_or(0 as usize, |v| *v);
        self.str_token.clear();
        PosRange { start, end }
    }

    pub fn skip_bc(&mut self) {
        while self.ch.as_ref().unwrap().ch == '\u{20}'
            || self.ch.as_ref().unwrap().ch == '\n'
            || self.ch.as_ref().unwrap().ch == '\r'
            || self.ch.as_ref().unwrap().ch == '\t'
        {
            self.get_char();
        }
    }

    pub fn is_digit(&self) -> bool {
        match &self.ch {
            Some(v) if '0' <= v.ch && v.ch <= '9' => {
                return true;
            },
            _ => return false,
        }
    }

    pub fn is_letter(&self) -> bool {
        if ('a' <= self.ch.as_ref().unwrap().ch && self.ch.as_ref().unwrap().ch <= 'z')
            || ('A' <= self.ch.as_ref().unwrap().ch && self.ch.as_ref().unwrap().ch <= 'Z')
        {
            return true;
        }
        return false;
    }

    //only support once now
    pub fn retract(&mut self) {
        self.bak_ch = self.ch.take();
        self.str_token.pop();
    }

    pub fn reserve(&mut self) {}

    pub fn insert_id(&mut self) {}

    pub fn insert_const(&mut self) {}
}