Struct itertools::Unfold

pub struct Unfold<St, F> {
    pub state: St,
    // some fields omitted
}

[−] Expand description

Unfold is a general iterator builder: it has a mutable state value, and a closure with access to the state that produces the next value.

This more or less equivalent to a regular struct with an Iterator implementation, and is useful for one-off iterators.

// an iterator that yields sequential Fibonacci numbers,
// and stops at the maximum representable value.

use itertools::Unfold;

let mut fibonacci = Unfold::new((1_u32, 1_u32), |state| {
    let (ref mut x1, ref mut x2) = *state;

    // Attempt to get the next Fibonacci number
    let next = x1.saturating_add(*x2);

    // Shift left: ret <- x1 <- x2 <- next
    let ret = *x1;
    *x1 = *x2;
    *x2 = next;

    // If addition has saturated at the maximum, we are finished
    if ret == *x1 && ret > 1 {
        return None;
    }

    Some(ret)
});

itertools::assert_equal(fibonacci.by_ref().take(8),
                        vec![1, 1, 2, 3, 5, 8, 13, 21]);
assert_eq!(fibonacci.last(), Some(2_971_215_073))

Fields

state: St

[−] Expand description

Internal state that will be passed to the closure on the next iteration

Methods

impl<A, St, F> Unfold<St, F> where F: FnMut(&mut St) -> Option<A>

fn new(initial_state: St, f: F) -> Unfold<St, F>[−]

Creates a new iterator with the specified closure as the "iterator function" and an initial state to eventually pass to the closure

Trait Implementations

impl<St: Clone, F: Clone> Clone for Unfold<St, F>

fn clone(&self) -> Unfold<St, F>[−]

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)[−]

Performs copy-assignment from source.

impl<A, St, F> Iterator for Unfold<St, F> where F: FnMut(&mut St) -> Option<A>

type Item = A

The type of the elements being iterated over.

fn next(&mut self) -> Option<A>[−]

Advances the iterator and returns the next value.

fn size_hint(&self) -> (usize, Option<usize>)[−]

Returns the bounds on the remaining length of the iterator.

fn count(self) -> usize[−]

Consumes the iterator, counting the number of iterations and returning it.

fn last(self) -> Option<Self::Item>[−]

Consumes the iterator, returning the last element.

fn nth(&mut self, n: usize) -> Option<Self::Item>[−]

Consumes the n first elements of the iterator, then returns the next() one.

fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item>[−]

Takes two iterators and creates a new iterator over both in sequence.

fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator[−]

'Zips up' two iterators into a single iterator of pairs.

fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B[−]

Takes a closure and creates an iterator which calls that closure on each element.

fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool[−]

Creates an iterator which uses a closure to determine if an element should be yielded.

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B>[−]

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>[−]

Creates an iterator which gives the current iteration count as well as the next value.

fn peekable(self) -> Peekable<Self>[−]

Creates an iterator which can use peek to look at the next element of the iterator without consuming it.

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool[−]

Creates an iterator that [skip()]s elements based on a predicate.

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool[−]

Creates an iterator that yields elements based on a predicate.

fn skip(self, n: usize) -> Skip<Self>[−]

Creates an iterator that skips the first n elements.

fn take(self, n: usize) -> Take<Self>[−]

Creates an iterator that yields its first n elements.

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B>[−]

An iterator adaptor similar to [fold()] that holds internal state and produces a new iterator.

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator[−]

Creates an iterator that works like map, but flattens nested structure.

fn fuse(self) -> Fuse<Self>[−]

Creates an iterator which ends after the first None.

fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> ()[−]

Do something with each element of an iterator, passing the value on.

fn by_ref(&mut self) -> &mut Self[−]

Borrows an iterator, rather than consuming it.

fn collect<B>(self) -> B where B: FromIterator<Self::Item>[−]

Transforms an iterator into a collection.

fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool[−]

Consumes an iterator, creating two collections from it.

fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B[−]

An iterator adaptor that applies a function, producing a single, final value.

fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool[−]

Tests if every element of the iterator matches a predicate.

fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool[−]

Tests if any element of the iterator matches a predicate.

fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool[−]

Searches for an element of an iterator that satisfies a predicate.

fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool[−]

Searches for an element in an iterator, returning its index.

fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool, Self: ExactSizeIterator + DoubleEndedIterator[−]

Searches for an element in an iterator from the right, returning its index.

fn max(self) -> Option<Self::Item> where Self::Item: Ord[−]

Returns the maximum element of an iterator.

fn min(self) -> Option<Self::Item> where Self::Item: Ord[−]

Returns the minimum element of an iterator.

fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B[−]

Returns the element that gives the maximum value from the specified function.

fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B[−]

Returns the element that gives the minimum value from the specified function.

fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator[−]

Reverses an iterator's direction.

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>, FromB: Default + Extend<B>, Self: Iterator<Item=(A, B)>[−]

Converts an iterator of pairs into a pair of containers.

fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone[−]

Creates an iterator which clone()s all of its elements.

fn cycle(self) -> Cycle<Self> where Self: Clone[−]

Repeats an iterator endlessly.

fn sum<S>(self) -> S where S: Sum<Self::Item>[−]

Sums the elements of an iterator.

fn product<P>(self) -> P where P: Product<Self::Item>[−]

Iterates over the entire iterator, multiplying all the elements

fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord[−]

Lexicographically compares the elements of this Iterator with those of another.

fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item>[−]

Lexicographically compares the elements of this Iterator with those of another.

fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>[−]

Determines if the elements of this Iterator are equal to those of another.

fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>[−]

Determines if the elements of this Iterator are unequal to those of another.

fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>[−]

Determines if the elements of this Iterator are lexicographically less than those of another.

fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>[−]

Determines if the elements of this Iterator are lexicographically less or equal to those of another.

fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>[−]

Determines if the elements of this Iterator are lexicographically greater than those of another.

fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>[−]

Determines if the elements of this Iterator are lexicographically greater than or equal to those of another.