use super::Itertools;
use super::misc::GenericRange;
/// A sliced iterator.
///
/// **Note:** slicing an iterator is not constant time, and much less efficient than
/// slicing for example a vector.
///
/// ## Example
/// ```
/// # extern crate itertools;
/// # fn main() {
/// use std::iter::repeat;
/// # use itertools::Itertools;
///
/// let mut it = repeat('a').slice(..3);
/// assert_eq!(it.count(), 3);
/// # }
/// ```
#[derive(Copy, Clone)]
pub struct ISlice<I> {
start: usize,
end: usize,
iter: I,
}
impl<I> ISlice<I>
where I: Iterator
{
/// Create a new **ISlice**.
pub fn new<R: GenericRange>(iter: I, range: R) -> Self
{
ISlice {
start: range.start().unwrap_or(0),
end: range.end().unwrap_or(::std::usize::MAX),
iter: iter,
}
}
}
impl<I> Iterator for ISlice<I>
where I: Iterator
{
type Item = I::Item;
fn next(&mut self) -> Option<I::Item>
{
if self.start != 0 {
let st = self.start;
let n = self.iter.dropn(self.start);
self.start = 0;
self.end -= n;
if n != st {
// iterator is already done.
return None
}
}
if self.end != 0 {
self.end -= 1;
self.iter.next()
} else {
None
}
}
}