Struct malachite_base::iterators::iterator_cache::IteratorCache

pub struct IteratorCache<I: Iterator> { /* private fields */ }

Remembers values produced by an iterator.

After wrapping an iterator with an IteratorCache, you can retrieve a reference to the $n$th element of an iterator, and then retrieve a reference to the $m$th element in constant time for any $m \leq n$ (not counting the time it took to first get the $n$th element).

Implementations

impl<I: Iterator> IteratorCache<I>

pub const fn new(xs: I) -> IteratorCache<I>

Creates a new IteratorCache.

This function does not allocate any memory or advance the iterator.

Worst-case complexity

Constant time and additional memory.

Examples

use malachite_base::iterators::iterator_cache::IteratorCache;

IteratorCache::new([1, 2, 3].iter());

pub fn get(&mut self, index: usize) -> Option<&I::Item>

Retrieves the $n$th element of an iterator. Indexing starts at 0.

If the index is higher than any other previously-requested index, the iterator is advanced to that index, or until it runs out. If the iterator has previously been advanced past the index, the requested element is returned from the cache in constant time. If the iterator is too short to have an element at the index, None is returned.

If you know that the element is present, and want to only take an immutable reference to self, consider using assert_get instead.

Worst-case complexity

$T(n) = O(n)$

$M(n) = O(n)$

where $T$ is time, $M$ is additional memory, and $n$ is 1 if get has previously been called with an index at least this large, or index otherwise.

Examples

use malachite_base::iterators::iterator_cache::IteratorCache;

let mut xs = IteratorCache::new([1, 2, 3].iter().cloned());
assert_eq!(xs.get(1), Some(&2));
assert_eq!(xs.get(0), Some(&1));
assert_eq!(xs.get(3), None);
assert_eq!(xs.get(2), Some(&3));

pub fn assert_get(&self, index: usize) -> &I::Item

Retrieves the $n$th element of an iterator, while asserting that the iterator has already reached that element. Indexing starts at 0.

If the iterator has not advanced that far, or if it has fewer than $n + 1$ elements, this function panics.

The purpose of this function is to allow the caller to get an element immutably, assuming that the caller knows that the element is present. The get function has to take a mutable reference.

Worst-case complexity

Constant time and additional memory.

Examples

use malachite_base::iterators::iterator_cache::IteratorCache;

let mut xs = IteratorCache::new([1, 2, 3].iter().cloned());
// Force the iterator to iterate to completion
xs.get(3);
assert_eq!(xs.assert_get(1), &2);
assert_eq!(xs.assert_get(0), &1);
assert_eq!(xs.assert_get(2), &3);

pub fn known_len(&self) -> Option<usize>

Returns the total number of elements in the iterator, if the iterator has been completely consumed.

If the iterator has not been completely consumed yet, returns None.

Worst-case complexity

Constant time and additional memory.

Examples

use malachite_base::iterators::iterator_cache::IteratorCache;

let mut xs = IteratorCache::new([1, 2, 3].iter().cloned());
assert_eq!(xs.known_len(), None);
assert_eq!(xs.get(1), Some(&2));
assert_eq!(xs.known_len(), None);
assert_eq!(xs.get(0), Some(&1));
assert_eq!(xs.get(3), None);
assert_eq!(xs.known_len(), Some(3));
assert_eq!(xs.get(2), Some(&3));

Trait Implementations

impl<I: Clone + Iterator> Clone for IteratorCache<I>

where I::Item: Clone,

fn clone(&self) -> IteratorCache<I>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<I: Debug + Iterator> Debug for IteratorCache<I>

where I::Item: Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.