Memory safety demo in Rust by Will Chrichton. Compile with `rustc -o memsafe memsafe.rs`

memsafe.rs

// http://willcrichton.net/notes/rust-memory-safety/
// Modified by Bart Massey 2018-02-03

#![feature(alloc, allocator_api)]

extern crate alloc;

use std::slice;
use std::heap::{Heap, Alloc};
use alloc::allocator::Layout;

struct Vec2 {
    data: Box<[isize]>,
    length: usize,
    capacity: usize
}

fn new() -> Vec2 {
    Vec2 {
        data: Box::new([]),
        length: 0,
        capacity: 0
    }
}

fn push(v: &mut Vec2, n: isize) {
    while v.length >= v.capacity {
        let new_capacity =
            if v.capacity == 0 {
                1
            } else {
                v.capacity * 2
            };
        let mut new_data = unsafe {
            let ptr = Heap::default()
                .alloc(Layout::array::<isize>(new_capacity).unwrap())
                .unwrap() as *mut isize;
            Box::from_raw(slice::from_raw_parts_mut(ptr, new_capacity))
        };

        for i in 0..v.length {
            new_data[i] = v.data[i];
        }

        v.data = new_data;
        v.capacity = new_capacity;
    }

    v.data[v.length] = n;
    v.length += 1;
}

fn main() {
    let mut vec = new();
    push(&mut vec, 107);
    let n = vec.data[0];
    push(&mut vec, 110);
    println!("{}", n);
}