# 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); } fn main() {}

    #![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);
    }