diff --git a/src/libcore/slice.rs b/src/libcore/slice.rs index 1e96d761d40..38e66c5a3d6 100644 --- a/src/libcore/slice.rs +++ b/src/libcore/slice.rs @@ -625,6 +625,36 @@ impl<'a, T> IntoIterator for &'a mut [T] { } } +#[inline(always)] +fn size_from_ptr(_: *const T) -> usize { + mem::size_of::() +} + + +// Use macro to be generic over const/mut +macro_rules! slice_offset { + ($ptr:expr, $by:expr) => {{ + let ptr = $ptr; + if size_from_ptr(ptr) == 0 { + transmute(ptr as usize + $by) + } else { + ptr.offset($by) + } + }}; +} + +macro_rules! slice_ref { + ($ptr:expr) => {{ + let ptr = $ptr; + if size_from_ptr(ptr) == 0 { + // Use a non-null pointer value + &mut *(1 as *mut _) + } else { + transmute(ptr) + } + }}; +} + // The shared definition of the `Iter` and `IterMut` iterators macro_rules! iterator { (struct $name:ident -> $ptr:ty, $elem:ty) => { @@ -641,20 +671,9 @@ macro_rules! iterator { if self.ptr == self.end { None } else { - if mem::size_of::() == 0 { - // purposefully don't use 'ptr.offset' because for - // vectors with 0-size elements this would return the - // same pointer. - self.ptr = transmute(self.ptr as usize + 1); - - // Use a non-null pointer value - Some(&mut *(1 as *mut _)) - } else { - let old = self.ptr; - self.ptr = self.ptr.offset(1); - - Some(transmute(old)) - } + let old = self.ptr; + self.ptr = slice_offset!(self.ptr, 1); + Some(slice_ref!(old)) } } } @@ -666,6 +685,22 @@ macro_rules! iterator { let exact = diff / (if size == 0 {1} else {size}); (exact, Some(exact)) } + + #[inline] + fn count(self) -> usize { + self.size_hint().0 + } + + #[inline] + fn nth(&mut self, n: usize) -> Option<$elem> { + // Call helper method. Can't put the definition here because mut versus const. + self.iter_nth(n) + } + + #[inline] + fn last(mut self) -> Option<$elem> { + self.next_back() + } } #[stable(feature = "rust1", since = "1.0.0")] @@ -679,17 +714,8 @@ macro_rules! iterator { if self.end == self.ptr { None } else { - if mem::size_of::() == 0 { - // See above for why 'ptr.offset' isn't used - self.end = transmute(self.end as usize - 1); - - // Use a non-null pointer value - Some(&mut *(1 as *mut _)) - } else { - self.end = self.end.offset(-1); - - Some(transmute(self.end)) - } + self.end = slice_offset!(self.end, -1); + Some(slice_ref!(self.end)) } } } @@ -785,6 +811,20 @@ impl<'a, T> Iter<'a, T> { pub fn as_slice(&self) -> &'a [T] { make_slice!(T => &'a [T]: self.ptr, self.end) } + + // Helper function for Iter::nth + fn iter_nth(&mut self, n: usize) -> Option<&'a T> { + match self.as_slice().get(n) { + Some(elem_ref) => unsafe { + self.ptr = slice_offset!(elem_ref as *const _, 1); + Some(slice_ref!(elem_ref)) + }, + None => { + self.ptr = self.end; + None + } + } + } } iterator!{struct Iter -> *const T, &'a T} @@ -914,6 +954,20 @@ impl<'a, T> IterMut<'a, T> { pub fn into_slice(self) -> &'a mut [T] { make_mut_slice!(T => &'a mut [T]: self.ptr, self.end) } + + // Helper function for IterMut::nth + fn iter_nth(&mut self, n: usize) -> Option<&'a mut T> { + match make_mut_slice!(T => &'a mut [T]: self.ptr, self.end).get_mut(n) { + Some(elem_ref) => unsafe { + self.ptr = slice_offset!(elem_ref as *mut _, 1); + Some(slice_ref!(elem_ref)) + }, + None => { + self.ptr = self.end; + None + } + } + } } iterator!{struct IterMut -> *mut T, &'a mut T} diff --git a/src/libcoretest/slice.rs b/src/libcoretest/slice.rs index fe73b3b4407..7c884a73ce0 100644 --- a/src/libcoretest/slice.rs +++ b/src/libcoretest/slice.rs @@ -82,3 +82,34 @@ fn iterator_to_slice() { test!([1u8,2,3]); test!([(),(),()]); } + +#[test] +fn test_iterator_nth() { + let v: &[_] = &[0, 1, 2, 3, 4]; + for i in 0..v.len() { + assert_eq!(v.iter().nth(i).unwrap(), &v[i]); + } + assert_eq!(v.iter().nth(v.len()), None); + + let mut iter = v.iter(); + assert_eq!(iter.nth(2).unwrap(), &v[2]); + assert_eq!(iter.nth(1).unwrap(), &v[4]); +} + +#[test] +fn test_iterator_last() { + let v: &[_] = &[0, 1, 2, 3, 4]; + assert_eq!(v.iter().last().unwrap(), &4); + assert_eq!(v[..1].iter().last().unwrap(), &0); +} + +#[test] +fn test_iterator_count() { + let v: &[_] = &[0, 1, 2, 3, 4]; + assert_eq!(v.iter().count(), 5); + + let mut iter2 = v.iter(); + iter2.next(); + iter2.next(); + assert_eq!(iter2.count(), 3); +}