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 queue. This queue allows us to peek at unconsumed elements (as far as the multi-peek iterator is concerned). When the iterator consumes an element, the element at the front of the queue will be dequeued, and will no longer be peekable.

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 to. If no such element exists, return None will be returned.

If we haven't advanced our cursor, it will point to the same element as Iterator::next() would return. Note that the cursor can't point to an element before the first unconsumed element within the iterator. In a sense the cursor moves independently within the iterator. But it can only point 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.

The example below primarily uses advance_cursor() to move the cursor and peek() to peek at the element the cursor points to, but many often more convenient methods exist to change the element cursor points at, or to peek at those elements.

• Let's 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()

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 the cursor.

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

// Calling `peek()` multiple times doesn't shift the position of the 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()

By calling next, the underlying iterator will be advanced andthe element represented by A will be consumed. It won't be possible to peek at A anymore.

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

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

• Call next().

The underlying iterator is advanced again. As a result, the cursor position also shifts to the next iterator position, which happens if the underlying iterator consumed an element where our cursor pointed at (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, an Err result containing a PeekMoreError::ElementHasBeenConsumed will be returned.

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.

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>

Advance the cursor to the next peekable element.

This method does not advance the iterator itself. To advance the iterator, call next() instead.

A mutable reference to the iterator is returned, which allows the operation to be chained.

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

Advance the cursor n elements forward.

This does not advance the iterator itself. To advance the iterator, call next() instead.

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

Moves the cursor forward until the predicate is no longer 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, a PeekMoreError::ElementHasBeenConsumed will be returned.

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, an error will be returned instead. 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 cursor position, the move_backward_or_reset method can be used.

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

Move the cursor n elements backward, or reset its position to the first non-consumed element. The latter happens when the cursor position is smaller than the elements it has to move backwards by.

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 peek is called just after a reset, it will return a reference to the first element.

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));

pub fn peek_range(&mut self, start: usize, end: usize) -> &[Option<I::Item>]

Returns a view into the next start (inclusive) to end (exclusive) elements.

Note: start and end represent indices and start at 0. These indices always start at the beginning of the queue (the unconsumed iterator) and don't take the position of the cursor into account.

Panics

Panics if start > end, in which case the range would be negative.

use peekmore::PeekMore;

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

match iter.peek_range(1, 3) {
    [Some(2), Some(p)] => println!("Yay! we found number {} after number 2", p),
    _ => println!("Oh noes!"),
}

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

Returns a view into the next n unconsumed elements of the iterator.

Here, n represents the amount of elements as counted from the start of the unconsumed iterator.

For example, if we created a (peekmore) iterator from the array [1, 2, 3] and consume the first element by calling the regular Iterator::next method, and then call peek_amount(3), the iterator will return &[Some(2), Some(3), None]. Here Some(2) and Some(3) are queued elements which we can peek at, and are not consumed by the iterator yet. None is the last element returned by our view, since our original iterator is sized and doesn't contain more elements. Thus in the absence of additional elements, we return None. This method is a variation on peek_range. You could instead have called peek_range(0, n) (note that peek_range takes indices as arguments instead of an amount).

Note: This method does not use or modify the position of the cursor.

Example:

use peekmore::PeekMore;

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

match iter.peek_amount(4) { // -> &[Option(&1), Option(&2), Option(&3), None]
  [Some(a), Some(b), Some(c), None] => println!("Found a match ({}, {}, {}) ", a, b, c),
  _ => eprintln!("Expected (just) 3 more values"),
}

Trait Implementations

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

pub fn clone(&self) -> PeekMoreIterator<I>

Returns a copy of the value.

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

Performs copy-assignment from source.

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

pub 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.

pub fn len(&self) -> usize

Returns the exact length of the iterator.

pub 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.

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

Advances the iterator and returns the next value.

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

Returns the bounds on the remaining length of the iterator.

pub fn count(self) -> usize

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

pub fn last(self) -> Option<Self::Item>

Consumes the iterator, returning the last element.

pub fn advance_by(&mut self, n: usize) -> Result<(), usize>

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

recently added

Advances the iterator by n elements.

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

Returns the nth element of the iterator.

pub 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.

pub 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.

pub 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.

pub 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.

pub fn for_each<F>(self, f: F) where
    F: FnMut(Self::Item), 

Calls a closure on each element of an iterator.

pub 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.

pub 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.

pub fn enumerate(self) -> Enumerate<Self>

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

pub fn peekable(self) -> Peekable<Self>

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

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

Creates an iterator that skips elements based on a predicate.

pub 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.

pub 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.

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

Creates an iterator that skips the first n elements.

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

Creates an iterator that yields its first n elements.

pub 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.

pub 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.

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

Creates an iterator that flattens nested structure.

pub fn fuse(self) -> Fuse<Self>

Creates an iterator which ends after the first None.

pub 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.

pub 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"]pub fn collect<B>(self) -> B where
    B: FromIterator<Self::Item>, 

Transforms an iterator into a collection.

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

Consumes an iterator, creating two collections from it.

pub fn partition_in_place<'a, T, P>(self, predicate: P) -> usize where
    Self: DoubleEndedIterator<Item = &'a mut T>,
    P: FnMut(&T) -> bool,
    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.

pub 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.

pub 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.

pub 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.

pub 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.

pub 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.

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

Tests if every element of the iterator matches a predicate.

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

Tests if any element of the iterator matches a predicate.

pub 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.

pub 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.

pub 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.

pub 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.

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

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

pub fn max(self) -> Option<Self::Item> where
    Self::Item: Ord, 

Returns the maximum element of an iterator.

pub fn min(self) -> Option<Self::Item> where
    Self::Item: Ord, 

Returns the minimum element of an iterator.

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

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

pub 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.

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

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

pub 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.

pub fn rev(self) -> Rev<Self> where
    Self: DoubleEndedIterator, 

Reverses an iterator's direction.

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

Converts an iterator of pairs into a pair of containers.

pub 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.

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

Creates an iterator which clones all of its elements.

pub fn cycle(self) -> Cycle<Self> where
    Self: Clone, 

Repeats an iterator endlessly.

pub fn sum<S>(self) -> S where
    S: Sum<Self::Item>, 

Sums the elements of an iterator.

pub fn product<P>(self) -> P where
    P: Product<Self::Item>, 

Iterates over the entire iterator, multiplying all the elements

pub 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.

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

🔬 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.

pub 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.

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

🔬 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.

pub 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.

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

🔬 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.

pub 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.

pub 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.

pub 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.

pub 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.

pub 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.

pub 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.

pub 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.

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