1.0.0[−][src]Trait std::iter::ExactSizeIterator
An iterator that knows its exact length.
Many Iterator
s don't know how many times they will iterate, but some do.
If an iterator knows how many times it can iterate, providing access to
that information can be useful. For example, if you want to iterate
backwards, a good start is to know where the end is.
When implementing an ExactSizeIterator
, you must also implement
Iterator
. When doing so, the implementation of size_hint
must
return the exact size of the iterator.
The len
method has a default implementation, so you usually shouldn't
implement it. However, you may be able to provide a more performant
implementation than the default, so overriding it in this case makes sense.
Examples
Basic usage:
// a finite range knows exactly how many times it will iterate let five = 0..5; assert_eq!(5, five.len());Run
In the module level docs, we implemented an Iterator
,
Counter
. Let's implement ExactSizeIterator
for it as well:
impl ExactSizeIterator for Counter { // We can easily calculate the remaining number of iterations. fn len(&self) -> usize { 5 - self.count } } // And now we can use it! let counter = Counter::new(); assert_eq!(5, counter.len());Run
Provided methods
fn len(&self) -> usize
Returns the exact number of times the iterator will iterate.
This method has a default implementation, so you usually should not implement it directly. However, if you can provide a more efficient implementation, you can do so. See the trait-level docs for an example.
This function has the same safety guarantees as the size_hint
function.
Examples
Basic usage:
// a finite range knows exactly how many times it will iterate let five = 0..5; assert_eq!(5, five.len());Run
fn is_empty(&self) -> bool
Returns true
if the iterator is empty.
This method has a default implementation using self.len()
, so you
don't need to implement it yourself.
Examples
Basic usage:
#![feature(exact_size_is_empty)] let mut one_element = std::iter::once(0); assert!(!one_element.is_empty()); assert_eq!(one_element.next(), Some(0)); assert!(one_element.is_empty()); assert_eq!(one_element.next(), None);Run
Implementations on Foreign Types
impl<K, V> ExactSizeIterator for IntoIter<K, V>
impl<'_, K> ExactSizeIterator for Drain<'_, K>
impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>
impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>
impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>
impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>
impl<'_, K, V> ExactSizeIterator for Drain<'_, K, V>
impl<'a, K> ExactSizeIterator for Iter<'a, K>
impl<K> ExactSizeIterator for IntoIter<K>
impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>
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Implementors
impl ExactSizeIterator for std::ascii::EscapeDefault
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impl ExactSizeIterator for EscapeDebug
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impl ExactSizeIterator for std::char::EscapeDefault
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impl ExactSizeIterator for EscapeUnicode
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impl ExactSizeIterator for ToLowercase
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impl ExactSizeIterator for ToUppercase
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impl ExactSizeIterator for Args
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impl ExactSizeIterator for ArgsOs
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impl ExactSizeIterator for Range<i16>
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impl ExactSizeIterator for Range<i32>
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impl ExactSizeIterator for Range<i8>
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impl ExactSizeIterator for Range<isize>
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impl ExactSizeIterator for Range<u16>
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impl ExactSizeIterator for Range<u32>
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impl ExactSizeIterator for Range<u8>
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impl ExactSizeIterator for Range<usize>
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impl ExactSizeIterator for RangeInclusive<i16>
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impl ExactSizeIterator for RangeInclusive<i8>
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impl ExactSizeIterator for RangeInclusive<u16>
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impl ExactSizeIterator for RangeInclusive<u8>
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impl<'_> ExactSizeIterator for Bytes<'_>
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impl<'_, A> ExactSizeIterator for std::option::Iter<'_, A>
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impl<'_, A> ExactSizeIterator for std::option::IterMut<'_, A>
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impl<'_, I> ExactSizeIterator for &'_ mut I where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<'_, I> ExactSizeIterator for Splice<'_, I> where
I: Iterator,
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I: Iterator,
impl<'_, K> ExactSizeIterator for std::collections::hash_set::Drain<'_, K>
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impl<'_, K> ExactSizeIterator for std::collections::hash_set::Iter<'_, K>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Iter<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::IterMut<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Keys<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Values<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::ValuesMut<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::Drain<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::Iter<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::IterMut<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::Keys<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::Values<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::ValuesMut<'_, K, V>
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impl<'_, T> ExactSizeIterator for std::collections::binary_heap::Drain<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::binary_heap::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::btree_set::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::linked_list::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::linked_list::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::vec_deque::Drain<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::vec_deque::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::collections::vec_deque::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for std::result::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::result::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for Chunks<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksExact<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksExactMut<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>
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impl<'_, T> ExactSizeIterator for std::slice::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::slice::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for RChunks<'_, T>
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impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, T>
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impl<'_, T> ExactSizeIterator for RChunksMut<'_, T>
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impl<'_, T> ExactSizeIterator for Windows<'_, T>
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impl<'_, T> ExactSizeIterator for std::vec::Drain<'_, T>
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impl<'a, I, T> ExactSizeIterator for Cloned<I> where
I: ExactSizeIterator<Item = &'a T>,
T: 'a + Clone,
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I: ExactSizeIterator<Item = &'a T>,
T: 'a + Clone,
impl<'a, I, T> ExactSizeIterator for Copied<I> where
I: ExactSizeIterator<Item = &'a T>,
T: 'a + Copy,
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I: ExactSizeIterator<Item = &'a T>,
T: 'a + Copy,
impl<'a, T> ExactSizeIterator for RChunksExact<'a, T>
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impl<A> ExactSizeIterator for std::option::IntoIter<A>
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impl<A, B> ExactSizeIterator for Zip<A, B> where
A: ExactSizeIterator,
B: ExactSizeIterator,
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A: ExactSizeIterator,
B: ExactSizeIterator,
impl<A, F> ExactSizeIterator for OnceWith<F> where
F: FnOnce() -> A,
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F: FnOnce() -> A,
impl<B, I, F> ExactSizeIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: ExactSizeIterator,
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F: FnMut(<I as Iterator>::Item) -> B,
I: ExactSizeIterator,
impl<I> ExactSizeIterator for Box<I> where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<I> ExactSizeIterator for Enumerate<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I> ExactSizeIterator for Fuse<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I> ExactSizeIterator for Peekable<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I> ExactSizeIterator for Rev<I> where
I: ExactSizeIterator + DoubleEndedIterator,
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I: ExactSizeIterator + DoubleEndedIterator,
impl<I> ExactSizeIterator for Skip<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I> ExactSizeIterator for StepBy<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I> ExactSizeIterator for Take<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
impl<I, F> ExactSizeIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item),
I: ExactSizeIterator,
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F: FnMut(&<I as Iterator>::Item),
I: ExactSizeIterator,