Struct Once

pub struct Once<T, E>(/* private fields */);

An iterator that yields something exactly once.

Trait Implementations

impl<T: Clone, E: Clone> Clone for Once<T, E>

fn clone(&self) -> Once<T, E>

Returns a copy of the value.

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

Performs copy-assignment from source.

impl<T: Debug, E: Debug> Debug for Once<T, E>

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

Formats the value using the given formatter.

impl<T, E> FallibleIterator for Once<T, E>

type Item = T

The type being iterated over.

type Error = E

The error type.

fn next(&mut self) -> Result<Option<Self::Item>, Self::Error>

Advances the iterator and returns the next value.

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

Returns bounds on the remaining length of the iterator.

fn count(self) -> Result<usize, Self::Error>

where Self: Sized,

Consumes the iterator, returning the number of remaining items.

fn last(self) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized,

Returns the last element of the iterator.

fn nth(&mut self, n: usize) -> Result<Option<Self::Item>, Self::Error>

Returns the nth element of the iterator.

fn step_by(self, step: usize) -> StepBy<Self>

where Self: Sized,

Returns an iterator starting at the same point, but stepping by the given amount at each iteration.

fn chain<I>(self, it: I) -> Chain<Self, I>

where I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>, Self: Sized,

Returns an iterator which yields the elements of this iterator followed by another.

fn zip<I>(self, o: I) -> Zip<Self, I::IntoFallibleIter>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>,

Returns an iterator that yields pairs of this iterator’s and another iterator’s values.

fn map<F, B>(self, f: F) -> Map<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> Result<B, Self::Error>,

Returns an iterator which applies a fallible transform to the elements of the underlying iterator.

fn for_each<F>(self, f: F) -> Result<(), Self::Error>

where Self: Sized, F: FnMut(Self::Item) -> Result<(), Self::Error>,

Calls a fallible closure on each element of an iterator.

fn filter<F>(self, f: F) -> Filter<Self, F>

where Self: Sized, F: FnMut(&Self::Item) -> Result<bool, Self::Error>,

Returns an iterator which uses a predicate to determine which values should be yielded. The predicate may fail; such failures are passed to the caller.

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F>

where Self: Sized, F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,

Returns an iterator which both filters and maps. The closure may fail; such failures are passed along to the consumer.

fn enumerate(self) -> Enumerate<Self>

where Self: Sized,

Returns an iterator which yields the current iteration count as well as the value.

fn peekable(self) -> Peekable<Self>

where Self: Sized,

Returns an iterator that can peek at the next element without consuming it.

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> Result<bool, Self::Error>,

Returns an iterator that skips elements based on a predicate.

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P>

where Self: Sized, P: FnMut(&Self::Item) -> Result<bool, Self::Error>,

Returns an iterator that yields elements based on a predicate.

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

where Self: Sized,

Returns an iterator which skips the first n values of this iterator.

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

where Self: Sized,

Returns an iterator that yields only the first n values of this iterator.

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F>

where Self: Sized, F: FnMut(&mut St, Self::Item) -> Result<Option<B>, Self::Error>,

Returns an iterator which applies a stateful map to values of this iterator.

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F>

where Self: Sized, U: IntoFallibleIterator<Error = Self::Error>, F: FnMut(Self::Item) -> Result<U, Self::Error>,

Returns an iterator which maps this iterator’s elements to iterators, yielding those iterators’ values.

fn flatten(self) -> Flatten<Self>

where Self: Sized, Self::Item: IntoFallibleIterator<Error = Self::Error>,

Returns an iterator which flattens an iterator of iterators, yielding those iterators’ values.

fn fuse(self) -> Fuse<Self>

where Self: Sized,

Returns an iterator which yields this iterator’s elements and ends after the first Ok(None).

fn inspect<F>(self, f: F) -> Inspect<Self, F>

where Self: Sized, F: FnMut(&Self::Item) -> Result<(), Self::Error>,

Returns an iterator which passes each element to a closure before returning it.

fn by_ref(&mut self) -> &mut Self

where Self: Sized,

Borrow an iterator rather than consuming it.

fn collect<T>(self) -> Result<T, Self::Error>

where T: FromIterator<Self::Item>, Self: Sized,

Transforms the iterator into a collection.

fn partition<B, F>(self, f: F) -> Result<(B, B), Self::Error>

where Self: Sized, B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> Result<bool, Self::Error>,

Transforms the iterator into two collections, partitioning elements by a closure.

fn fold<B, F>(self, init: B, f: F) -> Result<B, Self::Error>

where Self: Sized, F: FnMut(B, Self::Item) -> Result<B, Self::Error>,

Applies a function over the elements of the iterator, producing a single final value.

fn try_fold<B, E, F>(&mut self, init: B, f: F) -> Result<B, E>

where Self: Sized, E: From<Self::Error>, F: FnMut(B, Self::Item) -> Result<B, E>,

Applies a function over the elements of the iterator, producing a single final value.

fn all<F>(&mut self, f: F) -> Result<bool, Self::Error>

where Self: Sized, F: FnMut(Self::Item) -> Result<bool, Self::Error>,

Determines if all elements of this iterator match a predicate.

fn any<F>(&mut self, f: F) -> Result<bool, Self::Error>

where Self: Sized, F: FnMut(Self::Item) -> Result<bool, Self::Error>,

Determines if any element of this iterator matches a predicate.

fn find<F>(&mut self, f: F) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, F: FnMut(&Self::Item) -> Result<bool, Self::Error>,

Returns the first element of the iterator that matches a predicate.

fn find_map<B, F>(&mut self, f: F) -> Result<Option<B>, Self::Error>

where Self: Sized, F: FnMut(Self::Item) -> Result<Option<B>, Self::Error>,

Applies a function to the elements of the iterator, returning the first non-None result.

fn position<F>(&mut self, f: F) -> Result<Option<usize>, Self::Error>

where Self: Sized, F: FnMut(Self::Item) -> Result<bool, Self::Error>,

Returns the position of the first element of this iterator that matches a predicate. The predicate may fail; such failures are returned to the caller.

fn max(self) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, Self::Item: Ord,

Returns the maximal element of the iterator.

fn max_by_key<B, F>(self, f: F) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, B: Ord, F: FnMut(&Self::Item) -> Result<B, Self::Error>,

Returns the element of the iterator which gives the maximum value from the function.

fn max_by<F>(self, f: F) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,

Returns the element that gives the maximum value with respect to the function.

fn min(self) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, Self::Item: Ord,

Returns the minimal element of the iterator.

fn min_by_key<B, F>(self, f: F) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, B: Ord, F: FnMut(&Self::Item) -> Result<B, Self::Error>,

Returns the element of the iterator which gives the minimum value from the function.

fn min_by<F>(self, f: F) -> Result<Option<Self::Item>, Self::Error>

where Self: Sized, F: FnMut(&Self::Item, &Self::Item) -> Result<Ordering, Self::Error>,

Returns the element that gives the minimum value with respect to the function.

fn unzip<A, B, FromA, FromB>(self) -> Result<(FromA, FromB), Self::Error>

where Self: Sized + FallibleIterator<Item = (A, B)>, FromA: Default + Extend<A>, FromB: Default + Extend<B>,

Converts an iterator of pairs into a pair of containers.

fn cloned<'a, T>(self) -> Cloned<Self>

where Self: Sized + FallibleIterator<Item = &'a T>, T: 'a + Clone,

Returns an iterator which clones all of its elements.

fn cycle(self) -> Cycle<Self>

where Self: Sized + Clone,

Returns an iterator which repeats this iterator endlessly.

fn cmp<I>(self, other: I) -> Result<Ordering, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Item = Self::Item, Error = Self::Error>, Self::Item: Ord,

Lexicographically compares the elements of this iterator to that of another.

fn partial_cmp<I>(self, other: I) -> Result<Option<Ordering>, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, Self::Item: PartialOrd<I::Item>,

Lexicographically compares the elements of this iterator to that of another.

fn eq<I>(self, other: I) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, Self::Item: PartialEq<I::Item>,

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

fn ne<I>(self, other: I) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, Self::Item: PartialEq<I::Item>,

Determines if the elements of this iterator are not equal to those of another.

fn lt<I>(self, other: I) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, 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) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, Self::Item: PartialOrd<I::Item>,

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

fn gt<I>(self, other: I) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, 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) -> Result<bool, Self::Error>

where Self: Sized, I: IntoFallibleIterator<Error = Self::Error>, Self::Item: PartialOrd<I::Item>,

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

fn iterator(self) -> Iterator<Self>

where Self: Sized,

Returns a normal (non-fallible) iterator over Result<Item, Error>.

fn map_err<B, F>(self, f: F) -> MapErr<Self, F>

where F: FnMut(Self::Error) -> B, Self: Sized,

Returns an iterator which applies a transform to the errors of the underlying iterator.

fn unwrap<T>(self) -> Unwrap<Self>

where Self: Sized + FallibleIterator<Item = T>, Self::Error: Debug,

Returns an iterator which unwraps all of its elements.