1.0.0[−][src]Trait std::prelude::v1::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());
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());
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());
fn is_empty(&self) -> bool
exact_size_is_empty
)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);
Implementations on Foreign Types
impl<'_, I> ExactSizeIterator for &'_ mut I where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>
impl<'_, K> ExactSizeIterator for Drain<'_, K>
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 IntoIter<K, V>
impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>
impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>
impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>
impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>
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Implementors
impl ExactSizeIterator for ArgsOs
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impl ExactSizeIterator for Args
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impl ExactSizeIterator for EscapeDebug
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impl ExactSizeIterator for EscapeUnicode
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impl ExactSizeIterator for Range<usize>
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impl ExactSizeIterator for std::ascii::EscapeDefault
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impl ExactSizeIterator for Range<isize>
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impl ExactSizeIterator for ToLowercase
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impl ExactSizeIterator for std::char::EscapeDefault
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impl ExactSizeIterator for ToUppercase
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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<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 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 Splice<'_, I> where
I: Iterator,
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I: Iterator,
impl<'_, K> ExactSizeIterator for std::collections::hash_set::Iter<'_, K>
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impl<'_, K> ExactSizeIterator for std::collections::hash_set::Drain<'_, K>
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impl<'_, K, V> ExactSizeIterator for std::collections::hash_map::ValuesMut<'_, 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::Values<'_, 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::Keys<'_, K, V>
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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::Keys<'_, 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::btree_map::IterMut<'_, K, V>
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impl<'_, K, V> ExactSizeIterator for std::collections::btree_map::Values<'_, K, V>
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impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksExactMut<'_, T>
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impl<'_, T> ExactSizeIterator for Windows<'_, T>
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impl<'_, T> ExactSizeIterator for std::result::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for ChunksExact<'_, T>
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impl<'_, T> ExactSizeIterator for RChunks<'_, T>
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impl<'_, T> ExactSizeIterator for RChunksMut<'_, 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 std::slice::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for std::slice::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for std::vec::Drain<'_, T>
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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::vec_deque::IterMut<'_, 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::btree_set::Iter<'_, 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 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> ExactSizeIterator for Box<I> where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
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,