Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
- Loading branch information
1 parent
8bb5c66
commit 4750e7c
Showing
5 changed files
with
208 additions
and
0 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,127 @@ | ||
use size_hint; | ||
use std::collections::VecDeque; | ||
use std::iter::Fuse; | ||
use PeekingNext; | ||
|
||
/// See [`peek_nth()`](../fn.peek_nth.html) for more information. | ||
#[derive(Clone, Debug)] | ||
pub struct PeekNth<I> | ||
where | ||
I: Iterator, | ||
{ | ||
iter: Fuse<I>, | ||
buf: VecDeque<I::Item>, | ||
} | ||
|
||
/// A drop-in replacement for `std::iter::Peekable` which adds a `peek_nth` | ||
/// method allowing the user to `peek` at a value several iterations forward | ||
/// without advancing the base iterator. | ||
/// | ||
/// This differs from `multipeek` in that subsequent calls to `peek` or | ||
/// `peek_nth` will always return the same value until `next` is called | ||
/// (making `reset_peek` unnecessary). | ||
pub fn peek_nth<I>(iterable: I) -> PeekNth<I::IntoIter> | ||
where | ||
I: IntoIterator, | ||
{ | ||
return PeekNth { | ||
iter: iterable.into_iter().fuse(), | ||
buf: VecDeque::new(), | ||
}; | ||
} | ||
|
||
impl<I> PeekNth<I> | ||
where | ||
I: Iterator, | ||
{ | ||
/// Works exactly like the `peek` method in `std::iter::Peekable` | ||
pub fn peek(&mut self) -> Option<&I::Item> { | ||
return self.peek_nth(0); | ||
} | ||
|
||
/// Returns a reference to the `nth` value without advancing the iterator. | ||
/// | ||
/// # Examples | ||
/// | ||
/// Basic usage: | ||
/// | ||
/// ```rust | ||
/// use itertools::peek_nth; | ||
/// | ||
/// let xs = vec![1,2,3]; | ||
/// let mut iter = peek_nth(xs.iter()); | ||
/// | ||
/// assert_eq!(iter.peek_nth(0), Some(&&1)); | ||
/// assert_eq!(iter.next(), Some(&1)); | ||
/// | ||
/// // The iterator does not advance even if we call `peek_nth` multiple times | ||
/// assert_eq!(iter.peek_nth(0), Some(&&2)); | ||
/// assert_eq!(iter.peek_nth(1), Some(&&3)); | ||
/// assert_eq!(iter.next(), Some(&2)); | ||
/// | ||
/// // Calling `peek_nth` past the end of the iterator will return `None` | ||
/// assert_eq!(iter.peek_nth(1), None); | ||
/// ``` | ||
pub fn peek_nth(&mut self, n: usize) -> Option<&I::Item> { | ||
if n < self.buf.len() { | ||
return Some(&self.buf[n]); | ||
} | ||
|
||
for _ in self.buf.len()..(n + 1) { | ||
match self.iter.next() { | ||
Some(next_item) => { | ||
self.buf.push_back(next_item); | ||
} | ||
None => return None, | ||
} | ||
} | ||
|
||
return Some(&self.buf[n]); | ||
} | ||
} | ||
|
||
impl<I> Iterator for PeekNth<I> | ||
where | ||
I: Iterator, | ||
{ | ||
type Item = I::Item; | ||
|
||
fn next(&mut self) -> Option<I::Item> { | ||
if self.buf.is_empty() { | ||
return self.iter.next(); | ||
} else { | ||
return self.buf.pop_front(); | ||
} | ||
} | ||
|
||
fn size_hint(&self) -> (usize, Option<usize>) { | ||
return size_hint::add_scalar(self.iter.size_hint(), self.buf.len()); | ||
} | ||
} | ||
|
||
impl<I> ExactSizeIterator for PeekNth<I> where I: ExactSizeIterator {} | ||
|
||
impl<I> PeekingNext for PeekNth<I> | ||
where | ||
I: Iterator, | ||
{ | ||
fn peeking_next<F>(&mut self, accept: F) -> Option<Self::Item> | ||
where | ||
F: FnOnce(&Self::Item) -> bool, | ||
{ | ||
if self.buf.is_empty() { | ||
if let Some(r) = self.peek() { | ||
if !accept(r) { | ||
return None; | ||
} | ||
} | ||
} else { | ||
if let Some(r) = self.buf.get(0) { | ||
if !accept(r) { | ||
return None; | ||
} | ||
} | ||
} | ||
return self.next(); | ||
} | ||
} |
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters