Struct peekmore::PeekMoreIterator

pub struct PeekMoreIterator<I: Iterator> { /* fields omitted */ }

This iterator makes it possible to peek multiple times without consuming a value. In reality the underlying iterator will be consumed, but the values will be stored in a local queue. This queue allows us to move around unconsumed elements (as far as the iterator is concerned).

Implementations

impl<I: Iterator> PeekMoreIterator<I>

pub fn peek(&mut self) -> Option<&I::Item>

Get a reference to the element where the cursor currently points at (if such element exists). Sometimes we also call this the current 'view'.

If we haven't advanced our cursor, that will be the same element as the one next() would return, but if we have moved our cursor, it will be the element we moved to instead. Note that the cursor can't ever point at an element (which existed) before the first unconsumed element within the iterator. In a sense the cursor moves independently within the iterator. But it will always stick to unconsumed elements.

The following illustration aims to show how peek() behaves. i represents the position of the iterator (i.e. the next value that will be returned if next() is called) and j represents the position of the cursor (i.e. the current element referenced if peek() is called). In example code next to the illustrations, the first element 1 is analogous to A, 2 to B etc.

• start:

use peekmore::PeekMore;

// Initialize our iterator.
let iterable = [1, 2, 3, 4];
let mut iterator = iterable.iter().peekmore();

-----     -----      -----     -----
| A | --> | B |  --> | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
  ^
  i, j

• call peek():

let j = iterator.peek();
assert_eq!(j, Some(&&1));

-----     -----      -----     -----
| A | --> | B |  --> | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
  ^
  i, j
     returns Some(&A)

• call advance_cursor()

let iter = iterator.advance_cursor();

-----     -----      -----     -----
| A | --> | B |  --> | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
  ^         ^
  i         j

• call peek() or peek(); peek() or peek(); peek(); peek() etc.

(The reference returned by peek() will not change, similar to the behaviour of core::iter::Peekable::peek. In order to move to the next peekable element, we need to advance our view.)

let j = iterator.peek();
assert_eq!(j, Some(&&2));

// Calling peek() multiple times doesn't shift the position of our cursor;
// a reference to the same element will be returned each call.
assert_eq!(iterator.peek(), Some(&&2));
assert_eq!(iterator.peek(), Some(&&2));

-----     -----      -----     -----
| A | --> | B |  --> | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
  ^         ^
  i         j
            returns Some(&B)

• call next() (i.e. advance the iterator; the element represented by A will be consumed)

let i = iterator.next();
assert_eq!(i, Some(&1));

-----     -----      -----     -----
| A |     | B |  --> | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
            ^
            i, j
 returns Some(A)

• call next(). (i.e. advance the iterator again; we'll see that the cursor position shifts to the next iterator position if the iterator consumes elements where our cursor pointed at previously (that is if j < i))

// Show that the cursor still points at the second element.
let j = iterator.peek();
assert_eq!(j, Some(&&2));

// Consume the second element.
let i = iterator.next();
assert_eq!(i, Some(&2));

// Our cursor previously pointed at the element represented by B. Since that element has
// been consumed, the cursor shifts to the next unconsumed element: C.
let j = iterator.peek();
assert_eq!(j, Some(&&3));

-----     -----      -----     -----
| A |     | B |      | C | --> | D | --> None --> None --> ...
-----     -----      -----     -----
                       ^
                       i, j
          returns Some(B)

• Consume more elements by calling next() until we reach None:

let i = iterator.next();
assert_eq!(i, Some(&3));

let j = iterator.peek();
assert_eq!(j, Some(&&4));

let i = iterator.next();
assert_eq!(i, Some(&4));

let j = iterator.peek();
assert_eq!(j, None);

let i = iterator.next();
assert_eq!(i, None);

pub fn peek_next(&mut self) -> Option<&I::Item>

Advance the cursor to the next element and return a reference to that value.

pub fn peek_previous(&mut self) -> Result<Option<&I::Item>, PeekMoreError>

Try to peek at a previous element. If no such element exists (i.e. our cursor is already at the same point as the next iterator element), it will return an Err result containing a PeekMoreError::ElementHasBeenConsumed. If a previous element does exist, an option wrapped in an Ok result will be returned.

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

Move the cursor n steps forward and peek at the element the cursor then points to.

pub fn peek_backward(
    &mut self,
    n: usize
) -> Result<Option<&I::Item>, PeekMoreError>

Move the cursor n steps backward and peek at the element the cursor then points to.

If there aren't n elements prior to the element the cursor currently points at, a PeekMoreError::ElementHasBeenConsumed is returned instead. The cursor will then stay at the position it was prior to calling this method.

If you want to peek at the first unconsumed element instead of returning with an error, you can use the peek_backward_or_first method instead of this one.

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

Move the cursor n steps backward and peek at the element the cursor then points to, or if there aren't n elements prior to the element the cursor currently points to, peek at the first unconsumed element instead.

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

Peek at the nth element without moving the cursor.

pub fn advance_cursor(&mut self) -> &mut PeekMoreIterator<I>

Move the cursor to the next peekable element. This does not advance the iterator itself. To advance the iterator, use Iterator::next().

A mutable reference to the iterator is returned. This operation can be chained.

pub fn advance_cursor_by(&mut self, n: usize) -> &mut PeekMoreIterator<I>

Move the cursor n elements forward. This does not advance the iterator itself. To advance the iterator, use Iterator::next().

pub fn advance_cursor_while<P: Fn(Option<&I::Item>) -> bool>(
    &mut self,
    predicate: P
) -> &mut PeekMoreIterator<I>

Moves the cursor forward for as many elements as a predicate is true.

pub fn move_cursor_back(
    &mut self
) -> Result<&mut PeekMoreIterator<I>, PeekMoreError>

Move the cursor to the previous peekable element. If such an element doesn't exist, returns a PeekMoreError::ElementHasBeenConsumed.

If we can move to a previous element, a mutable reference to the iterator, wrapped in the Ok variant of Result will be returned.

pub fn move_cursor_back_by(
    &mut self,
    n: usize
) -> Result<&mut PeekMoreIterator<I>, PeekMoreError>

Move the cursor n elements backward. If there aren't n unconsumed elements prior to the cursor it will return an error. In case of an error, the cursor will stay at the position it pointed at prior to calling this method.

If you want to reset the cursor to the first unconsumed element even if there aren't n unconsumed elements before the position the cursor points at, you can use the move_backward_or_reset method instead.

pub fn move_cursor_back_or_reset(
    &mut self,
    n: usize
) -> &mut PeekMoreIterator<I>

Move the cursor n elements backward or reset to the first non consumed element if we can't move the cursor n elements to the back.

pub fn move_nth(&mut self, n: usize) -> &mut PeekMoreIterator<I>

Move the cursor to the n-th element of the queue.

pub fn reset_view(&mut self)

👎 Deprecated

Deprecated: use reset_cursor instead.

pub fn reset_cursor(&mut self)

Reset the position of the cursor. If we call peek just after a reset, it will return a reference to the first element again.

pub fn truncate_iterator_to_cursor(&mut self)

Remove all elements from the start of the iterator until reaching the same position as the cursor by calling Iterator::next()

After calling this method, iter.peek() == iter.next().as_ref()

 use peekmore::PeekMore;

 let iterable = [1, 2, 3, 4];
 let mut iter = iterable.iter().peekmore();

 iter.advance_cursor_by(2);
 assert_eq!(iter.peek(), Some(&&3));
 assert_eq!(iter.next(), Some(&1));
 iter.truncate_iterator_to_cursor();
 assert_eq!(iter.peek(), Some(&&3));
 assert_eq!(iter.next(), Some(&3));

Trait Implementations

impl<I: Clone + Iterator> Clone for PeekMoreIterator<I> where
    I::Item: Clone, 

fn clone(&self) -> PeekMoreIterator<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 PeekMoreIterator<I> where
    I::Item: Debug, 

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

Formats the value using the given formatter.

impl<I: ExactSizeIterator> ExactSizeIterator for PeekMoreIterator<I>

Uses ExactSizeIterator default implementation.

fn len(&self) -> usize

Returns the exact length of the iterator.

fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (exact_size_is_empty)

Returns true if the iterator is empty.

impl<I: FusedIterator> FusedIterator for PeekMoreIterator<I>

Uses FusedIterator default implementation.

impl<'a, I: Iterator> Iterator for PeekMoreIterator<I>

type Item = I::Item

The type of the elements being iterated over.

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

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>

Returns the nth element of the iterator.

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

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

fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::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 as IntoIterator>::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 for_each<F>(self, f: F) where
    F: FnMut(Self::Item), 

Calls a closure on each element of an iterator.

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 map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> where
    P: FnMut(Self::Item) -> Option<B>, 

🔬 This is a nightly-only experimental API. (iter_map_while)

recently added

Creates an iterator that both yields elements based on a predicate and maps.

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 flatten(self) -> Flatten<Self> where
    Self::Item: IntoIterator, 

Creates an iterator that 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), 

Does 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.

#[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"]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 partition_in_place<'a, T, P>(self, predicate: P) -> usize where
    P: FnMut(&T) -> bool,
    Self: DoubleEndedIterator<Item = &'a mut T>,
    T: 'a, 

🔬 This is a nightly-only experimental API. (iter_partition_in_place)

new API

Reorders the elements of this iterator in-place according to the given predicate, such that all those that return true precede all those that return false. Returns the number of true elements found.

fn is_partitioned<P>(self, predicate: P) -> bool where
    P: FnMut(Self::Item) -> bool, 

🔬 This is a nightly-only experimental API. (iter_is_partitioned)

new API

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false.

fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
    F: FnMut(B, Self::Item) -> R,
    R: Try<Ok = B>, 

An iterator method that applies a function as long as it returns successfully, producing a single, final value.

fn try_for_each<F, R>(&mut self, f: F) -> R where
    F: FnMut(Self::Item) -> R,
    R: Try<Ok = ()>, 

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error.

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

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

fn fold_first<F>(self, f: F) -> Option<Self::Item> where
    F: FnMut(Self::Item, Self::Item) -> Self::Item, 

🔬 This is a nightly-only experimental API. (iterator_fold_self)

The same as fold(), but uses the first element in the iterator as the initial value, folding every subsequent element into it. If the iterator is empty, return None; otherwise, return the result of the fold.

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 find_map<B, F>(&mut self, f: F) -> Option<B> where
    F: FnMut(Self::Item) -> Option<B>, 

Applies function to the elements of iterator and returns the first non-none result.

fn try_find<F, R>(
    &mut self,
    f: F
) -> Result<Option<Self::Item>, <R as Try>::Error> where
    F: FnMut(&Self::Item) -> R,
    R: Try<Ok = bool>, 

🔬 This is a nightly-only experimental API. (try_find)

new API

Applies function to the elements of iterator and returns the first true result or the first error.

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 max_by<F>(self, compare: F) -> Option<Self::Item> where
    F: FnMut(&Self::Item, &Self::Item) -> Ordering, 

Returns the element that gives the maximum value with respect to the specified comparison 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 min_by<F>(self, compare: F) -> Option<Self::Item> where
    F: FnMut(&Self::Item, &Self::Item) -> Ordering, 

Returns the element that gives the minimum value with respect to the specified comparison 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 copied<'a, T>(self) -> Copied<Self> where
    Self: Iterator<Item = &'a T>,
    T: 'a + Copy, 

Creates an iterator which copies all of its elements.

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 cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where
    F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,
    I: IntoIterator, 

🔬 This is a nightly-only experimental API. (iter_order_by)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

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

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

fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering> where
    F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,
    I: IntoIterator, 

🔬 This is a nightly-only experimental API. (iter_order_by)

Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function.

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

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

fn eq_by<I, F>(self, other: I, eq: F) -> bool where
    F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,
    I: IntoIterator, 

🔬 This is a nightly-only experimental API. (iter_order_by)

Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function.

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

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

fn is_sorted(self) -> bool where
    Self::Item: PartialOrd<Self::Item>, 

🔬 This is a nightly-only experimental API. (is_sorted)

new API

Checks if the elements of this iterator are sorted.

fn is_sorted_by<F>(self, compare: F) -> bool where
    F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>, 

🔬 This is a nightly-only experimental API. (is_sorted)

new API

Checks if the elements of this iterator are sorted using the given comparator function.

fn is_sorted_by_key<F, K>(self, f: F) -> bool where
    F: FnMut(Self::Item) -> K,
    K: PartialOrd<K>, 

🔬 This is a nightly-only experimental API. (is_sorted)

new API

Checks if the elements of this iterator are sorted using the given key extraction function.