Shared via Rust Playground

playground.rs

//#![feature(question_mark)]

use std::ops::Deref;
use std::ops::DerefMut;

#[derive(Debug, Default)]
struct ReuseBuf {
    inner: Vec<u32>,
    used: bool
}

impl ReuseBuf {
    pub fn new() -> ReuseBuf {
        Default::default()
    }
    
    pub fn get_buf<'a>(& 'a mut self) -> Buf<'a> {
       assert!(!self.used);
       assert!(self.inner.is_empty());
       self.used = true;
       Buf { inner: self }
    }
}

#[derive(Debug)]
struct Buf<'a> {
    inner: &'a mut ReuseBuf,
}

impl<'a> Deref for Buf<'a> {
    type Target=Vec<u32>;
    fn deref(&self) -> & Vec<u32> {
        &self.inner.inner
    }
}


impl<'a> DerefMut for Buf<'a> {
    fn deref_mut(&mut self) -> &mut Vec<u32> {
        &mut self.inner.inner
    }
}


impl<'a> Drop for Buf<'a> {
    fn drop(&mut self) {
        self.inner.used = false;
        self.inner.inner.clear();
    }
}

fn main2() {
    let mut buf = ReuseBuf::new();
    
    println!("Printing stuff {:?}", buf);
 
    {
       let ref mut b1 = *buf.get_buf();
       b1.push(1);
       b1.push(2);
       println!("Printing stuff {:?}", b1);
       // let mut b2 = buf.get_buf();
       // b2.push(1);
       // b2.push(2);
       // println!("Printing stuff {:?}, {:?}", b2, *b2);
    }

    println!("Printing stuff {:?}", buf);
 
    {
       let mut b1 = buf.get_buf();
       b1.push(3);
       println!("Printing stuff {:?}, {:?}", b1, *b1);
    }
    
    println!("Printing stuff {:?}", buf);
}

fn main() {main2();}