1. 1. Introduction
  2. 2. Meet Safe and Unsafe
    1. 2.1. How Safe and Unsafe Interact
    2. 2.2. Working with Unsafe
  3. 3. Data Layout
    1. 3.1. repr(Rust)
    2. 3.2. Exotically Sized Types
    3. 3.3. Other reprs
  4. 4. Ownership
    1. 4.1. References
    2. 4.2. Lifetimes
    3. 4.3. Limits of Lifetimes
    4. 4.4. Lifetime Elision
    5. 4.5. Unbounded Lifetimes
    6. 4.6. Higher-Rank Trait Bounds
    7. 4.7. Subtyping and Variance
    8. 4.8. Drop Check
    9. 4.9. PhantomData
    10. 4.10. Splitting Borrows
  5. 5. Type Conversions
    1. 5.1. Coercions
    2. 5.2. The Dot Operator
    3. 5.3. Casts
    4. 5.4. Transmutes
  6. 6. Uninitialized Memory
    1. 6.1. Checked
    2. 6.2. Drop Flags
    3. 6.3. Unchecked
  7. 7. Ownership Based Resource Management
    1. 7.1. Constructors
    2. 7.2. Destructors
    3. 7.3. Leaking
  8. 8. Unwinding
    1. 8.1. Exception Safety
    2. 8.2. Poisoning
  9. 9. Concurrency
    1. 9.1. Races
    2. 9.2. Send and Sync
    3. 9.3. Atomics
  10. 10. Implementing Vec
    1. 10.1. Layout
    2. 10.2. Allocating
    3. 10.3. Push and Pop
    4. 10.4. Deallocating
    5. 10.5. Deref
    6. 10.6. Insert and Remove
    7. 10.7. IntoIter
    8. 10.8. RawVec
    9. 10.9. Drain
    10. 10.10. Handling Zero-Sized Types
    11. 10.11. Final Code
  11. 11. Implementing Arc and Mutex

The Final Code

#![feature(unique)]
#![feature(alloc, heap_api)]

extern crate alloc;

use std::ptr::{Unique, self};
use std::mem;
use std::ops::{Deref, DerefMut};
use std::marker::PhantomData;

use alloc::heap;

struct RawVec<T> {
    ptr: Unique<T>,
    cap: usize,
}

impl<T> RawVec<T> {
    fn new() -> Self {
        unsafe {
            // !0 is usize::MAX. This branch should be stripped at compile time.
            let cap = if mem::size_of::<T>() == 0 { !0 } else { 0 };

            // heap::EMPTY doubles as "unallocated" and "zero-sized allocation"
            RawVec { ptr: Unique::new(heap::EMPTY as *mut T), cap: cap }
        }
    }

    fn grow(&mut self) {
        unsafe {
            let elem_size = mem::size_of::<T>();

            // since we set the capacity to usize::MAX when elem_size is
            // 0, getting to here necessarily means the Vec is overfull.
            assert!(elem_size != 0, "capacity overflow");

            let align = mem::align_of::<T>();

            let (new_cap, ptr) = if self.cap == 0 {
                let ptr = heap::allocate(elem_size, align);
                (1, ptr)
            } else {
                let new_cap = 2 * self.cap;
                let ptr = heap::reallocate(*self.ptr as *mut _,
                                            self.cap * elem_size,
                                            new_cap * elem_size,
                                            align);
                (new_cap, ptr)
            };

            // If allocate or reallocate fail, we'll get `null` back
            if ptr.is_null() { oom() }

            self.ptr = Unique::new(ptr as *mut _);
            self.cap = new_cap;
        }
    }
}

impl<T> Drop for RawVec<T> {
    fn drop(&mut self) {
        let elem_size = mem::size_of::<T>();
        if self.cap != 0 && elem_size != 0 {
            let align = mem::align_of::<T>();

            let num_bytes = elem_size * self.cap;
            unsafe {
                heap::deallocate(*self.ptr as *mut _, num_bytes, align);
            }
        }
    }
}





pub struct Vec<T> {
    buf: RawVec<T>,
    len: usize,
}

impl<T> Vec<T> {
    fn ptr(&self) -> *mut T { *self.buf.ptr }

    fn cap(&self) -> usize { self.buf.cap }

    pub fn new() -> Self {
        Vec { buf: RawVec::new(), len: 0 }
    }
    pub fn push(&mut self, elem: T) {
        if self.len == self.cap() { self.buf.grow(); }

        unsafe {
            ptr::write(self.ptr().offset(self.len as isize), elem);
        }

        // Can't fail, we'll OOM first.
        self.len += 1;
    }

    pub fn pop(&mut self) -> Option<T> {
        if self.len == 0 {
            None
        } else {
            self.len -= 1;
            unsafe {
                Some(ptr::read(self.ptr().offset(self.len as isize)))
            }
        }
    }

    pub fn insert(&mut self, index: usize, elem: T) {
        assert!(index <= self.len, "index out of bounds");
        if self.cap() == self.len { self.buf.grow(); }

        unsafe {
            if index < self.len {
                ptr::copy(self.ptr().offset(index as isize),
                          self.ptr().offset(index as isize + 1),
                          self.len - index);
            }
            ptr::write(self.ptr().offset(index as isize), elem);
            self.len += 1;
        }
    }

    pub fn remove(&mut self, index: usize) -> T {
        assert!(index < self.len, "index out of bounds");
        unsafe {
            self.len -= 1;
            let result = ptr::read(self.ptr().offset(index as isize));
            ptr::copy(self.ptr().offset(index as isize + 1),
                      self.ptr().offset(index as isize),
                      self.len - index);
            result
        }
    }

    pub fn into_iter(self) -> IntoIter<T> {
        unsafe {
            let iter = RawValIter::new(&self);
            let buf = ptr::read(&self.buf);
            mem::forget(self);

            IntoIter {
                iter: iter,
                _buf: buf,
            }
        }
    }

    pub fn drain(&mut self) -> Drain<T> {
        unsafe {
            let iter = RawValIter::new(&self);

            // this is a mem::forget safety thing. If Drain is forgotten, we just
            // leak the whole Vec's contents. Also we need to do this *eventually*
            // anyway, so why not do it now?
            self.len = 0;

            Drain {
                iter: iter,
                vec: PhantomData,
            }
        }
    }
}

impl<T> Drop for Vec<T> {
    fn drop(&mut self) {
        while let Some(_) = self.pop() {}
        // allocation is handled by RawVec
    }
}

impl<T> Deref for Vec<T> {
    type Target = [T];
    fn deref(&self) -> &[T] {
        unsafe {
            ::std::slice::from_raw_parts(self.ptr(), self.len)
        }
    }
}

impl<T> DerefMut for Vec<T> {
    fn deref_mut(&mut self) -> &mut [T] {
        unsafe {
            ::std::slice::from_raw_parts_mut(self.ptr(), self.len)
        }
    }
}





struct RawValIter<T> {
    start: *const T,
    end: *const T,
}

impl<T> RawValIter<T> {
    unsafe fn new(slice: &[T]) -> Self {
        RawValIter {
            start: slice.as_ptr(),
            end: if mem::size_of::<T>() == 0 {
                ((slice.as_ptr() as usize) + slice.len()) as *const _
            } else if slice.len() == 0 {
                slice.as_ptr()
            } else {
                slice.as_ptr().offset(slice.len() as isize)
            }
        }
    }
}

impl<T> Iterator for RawValIter<T> {
    type Item = T;
    fn next(&mut self) -> Option<T> {
        if self.start == self.end {
            None
        } else {
            unsafe {
                let result = ptr::read(self.start);
                self.start = if mem::size_of::<T>() == 0 {
                    (self.start as usize + 1) as *const _
                } else {
                    self.start.offset(1)
                };
                Some(result)
            }
        }
    }

    fn size_hint(&self) -> (usize, Option<usize>) {
        let elem_size = mem::size_of::<T>();
        let len = (self.end as usize - self.start as usize)
                  / if elem_size == 0 { 1 } else { elem_size };
        (len, Some(len))
    }
}

impl<T> DoubleEndedIterator for RawValIter<T> {
    fn next_back(&mut self) -> Option<T> {
        if self.start == self.end {
            None
        } else {
            unsafe {
                self.end = if mem::size_of::<T>() == 0 {
                    (self.end as usize - 1) as *const _
                } else {
                    self.end.offset(-1)
                };
                Some(ptr::read(self.end))
            }
        }
    }
}




pub struct IntoIter<T> {
    _buf: RawVec<T>, // we don't actually care about this. Just need it to live.
    iter: RawValIter<T>,
}

impl<T> Iterator for IntoIter<T> {
    type Item = T;
    fn next(&mut self) -> Option<T> { self.iter.next() }
    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
}

impl<T> DoubleEndedIterator for IntoIter<T> {
    fn next_back(&mut self) -> Option<T> { self.iter.next_back() }
}

impl<T> Drop for IntoIter<T> {
    fn drop(&mut self) {
        for _ in &mut *self {}
    }
}




pub struct Drain<'a, T: 'a> {
    vec: PhantomData<&'a mut Vec<T>>,
    iter: RawValIter<T>,
}

impl<'a, T> Iterator for Drain<'a, T> {
    type Item = T;
    fn next(&mut self) -> Option<T> { self.iter.next_back() }
    fn size_hint(&self) -> (usize, Option<usize>) { self.iter.size_hint() }
}

impl<'a, T> DoubleEndedIterator for Drain<'a, T> {
    fn next_back(&mut self) -> Option<T> { self.iter.next_back() }
}

impl<'a, T> Drop for Drain<'a, T> {
    fn drop(&mut self) {
        // pre-drain the iter
        for _ in &mut self.iter {}
    }
}

/// Abort the process, we're out of memory!
///
/// In practice this is probably dead code on most OSes
fn oom() {
    ::std::process::exit(-9999);
}
Run