/// An owned, partially type-converted vector.
///
+/// This struct takes two type parameters `T` and `U` which must be of the
+/// same, non-zero size.
+///
/// No allocations are performed by usage, only a deallocation happens in the
/// destructor which should only run when unwinding.
///
/// # Example
///
/// ```rust
-/// let pv = PartialVec::new(vec![0u, 1]);
+/// let pv = PartialVec::from_vec(vec![0u, 1]);
/// assert_eq!(pv.pop(), Some(0));
/// assert_eq!(pv.pop(), Some(1));
/// assert_eq!(pv.pop(), None);
/// pv.push(2u);
/// pv.push(3);
-/// assert_eq!(pv.into_vec(), vec![2, 3]);
+/// assert_eq!(pv.into_vec().as_slice(), &[2, 3]);
/// ```
//
// Upheld invariants:
//
// (f) From `start_t` (incl.) to `end_t` (excl.) there are sequential instances
// of type `T`.
+//
+// (g) The size of `T` and `U` is equal and non-zero.
pub struct PartialVec<T,U> {
vec: Vec<T>,
impl<T,U> PartialVec<T,U> {
/// Creates a `PartialVec` from a `Vec`.
- pub fn new(mut vec: Vec<T>) -> PartialVec<T,U> {
+ ///
+ /// # Failure
+ ///
+ /// Fails if `T` and `U` have differing sizes or are zero-sized.
+ pub fn from_vec(mut vec: Vec<T>) -> PartialVec<T,U> {
// FIXME: Assert that the types `T` and `U` have the same size.
+ //
+ // These asserts make sure (g) is satisfied.
assert!(mem::size_of::<T>() != 0);
assert!(mem::size_of::<U>() != 0);
assert!(mem::size_of::<T>() == mem::size_of::<U>());
let start_u = start as *mut U;
let end_u = start as *mut U;
let start_t = start;
+
+ // This points inside the vector, as the vector has length `offset`.
let end_t = unsafe { start_t.offset(offset) };
// (b) is satisfied, `start_u` points to the start of `vec`.
-
+ //
// (c) is also satisfied, `end_t` points to the end of `vec`.
-
+ //
// `start_u == end_u == start_t <= end_t`, so also `start_u <= end_u <=
// start_t <= end_t`, thus (b).
-
+ //
// As `start_u == end_u`, it is represented correctly that there are no
// instances of `U` in `vec`, thus (e) is satisfied.
-
+ //
// At start, there are only elements of type `T` in `vec`, so (f) is
// satisfied, as `start_t` points to the start of `vec` and `end_t` to
// the end of it.
- // This points inside the vector, as the vector has length `offset`.
-
PartialVec {
// (a) is satisfied, `vec` isn't modified in the function.
vec: vec,
/// Pops a `T` from the `PartialVec`.
///
- /// Returns `Some(t)` if there are more `T`s in the vector, otherwise
- /// `None`.
+ /// Removes the next `T` from the vector and returns it as `Some(T)`, or
+ /// `None` if there are none left.
fn pop(&mut self) -> Option<T> {
// The `if` ensures that there are more `T`s in `vec`.
if self.start_t < self.end_t {
///
/// Fails if not all `T`s were popped, also fails if not the same amount of
/// `U`s was pushed before calling `unwrap`.
- pub fn into_vec(self) -> Vec<U> {
+ pub fn into_vec(mut self) -> Vec<U> {
// If `self.end_u == self.end_t`, we know from (e) that there are no
// more `T`s in `vec`, we also know that the whole length of `vec` is
- // now used by `U`s, thus we can just transmute `vec` from a vector of
- // `T`s to a vector of `U`s safely.
+ // now used by `U`s, thus we can just interpret `vec` as a vector of
+ // `U` safely.
assert!(self.end_u as *const () == self.end_t as *const (),
"trying to unwrap a PartialVec before completing the writes to it");
// Extract `vec` and prevent the destructor of `PartialVec` from
- // running.
+ // running. Note that none of the function calls can fail, thus no
+ // resources can be leaked (as the `vec` member of `PartialVec` is the
+ // only one which holds allocations -- and it is returned from this
+ // function.
unsafe {
- let vec = ptr::read(&self.vec);
+ let vec_len = self.vec.len();
+ let vec_cap = self.vec.capacity();
+ let vec_ptr = self.vec.as_mut_ptr() as *mut U;
mem::forget(self);
- mem::transmute(vec)
+ Vec::from_raw_parts(vec_len, vec_cap, vec_ptr)
}
}
}
}
impl<T> Vec<T> {
- /// Converts a `Vec<T>` to a `Vec<U>` where `T` and `U` have the same size.
+ /// Converts a `Vec<T>` to a `Vec<U>` where `T` and `U` have the same
+ /// non-zero size.
+ ///
+ /// # Failure
+ ///
+ /// Fails if `T` and `U` have differing sizes or are zero-sized.
///
/// # Example
///
/// ```rust
/// let v = vec![0u, 1, 2];
/// let w = v.map_inplace(|i| i + 3);
- /// assert_eq!(w.as_slice() == &[3, 4, 5]);
+ /// assert_eq!(w.as_slice(), &[3, 4, 5]);
///
/// let big_endian_u16s = vec![0x1122u16, 0x3344];
/// let u8s = big_endian_u16s.map_inplace(|x| [
/// ((x >> 8) & 0xff) as u8,
/// (x & 0xff) as u8
/// ]);
- /// assert_eq!(u8s.as_slice() == &[[0x11, 0x22], [0x33, 0x44]]);
+ /// assert_eq!(u8s.as_slice(), &[[0x11, 0x22], [0x33, 0x44]]);
/// ```
pub fn map_inplace<U>(self, f: |T| -> U) -> Vec<U> {
- let mut pv = PartialVec::new(self);
+ let mut pv = PartialVec::from_vec(self);
loop {
let maybe_t = pv.pop();
match maybe_t {
#[test]
fn test_map_inplace() {
let v = vec![0u, 1, 2];
- assert_eq!(v.map_inplace(|i: uint| i as int - 1).as_slice, &[-1i, 0, 1]);
+ assert_eq!(v.map_inplace(|i: uint| i as int - 1).as_slice(), &[-1i, 0, 1]);
}
#[bench]
projects / rust.git / blobdiff