Trait stdcli::prelude::itertools::__std_iter::ExactSizeIterator 1.0.0
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pub trait ExactSizeIterator: Iterator { fn len(&self) -> usize { ... } fn is_empty(&self) -> bool { ... } }
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 whether 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 = 0..1; 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<V> ExactSizeIterator for IntoIter<V>
impl<'a, V> ExactSizeIterator for Keys<'a, V>
impl<'a, V> ExactSizeIterator for IterMut<'a, V>
impl<'a, V> ExactSizeIterator for Values<'a, V>
impl<'a, V> ExactSizeIterator for Iter<'a, V>
impl<'a, V> ExactSizeIterator for Drain<'a, V>
impl ExactSizeIterator for Range<i32>
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impl<'a, I> ExactSizeIterator for &'a mut I where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<'a, A> ExactSizeIterator for IterMut<'a, A>
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impl ExactSizeIterator for RangeInclusive<u8>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, T> ExactSizeIterator for ChunksMut<'a, T>
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impl ExactSizeIterator for Range<usize>
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impl ExactSizeIterator for EscapeDefault
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impl ExactSizeIterator for Range<i8>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, T> ExactSizeIterator for IterMut<'a, T>
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impl ExactSizeIterator for RangeInclusive<i16>
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impl<T> ExactSizeIterator for IntoIter<T>
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impl<'a, T> ExactSizeIterator for Windows<'a, T>
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impl ExactSizeIterator for Range<i16>
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impl ExactSizeIterator for Range<isize>
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impl ExactSizeIterator for Range<u32>
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impl<'a, A> ExactSizeIterator for Iter<'a, A>
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impl ExactSizeIterator for RangeInclusive<u16>
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impl ExactSizeIterator for Range<u16>
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impl<'a, T> ExactSizeIterator for IterMut<'a, T>
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impl<A> ExactSizeIterator for IntoIter<A>
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impl ExactSizeIterator for EscapeUnicode
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impl<'a> ExactSizeIterator for Bytes<'a>
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impl ExactSizeIterator for RangeInclusive<i8>
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impl ExactSizeIterator for EscapeDebug
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impl<'a, T> ExactSizeIterator for Chunks<'a, T>
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impl ExactSizeIterator for Range<u8>
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impl<'a, T> ExactSizeIterator for Drain<'a, T>
impl<A> ExactSizeIterator for IntoIter<A> where
A: Array,
A: Array,
impl<T> ExactSizeIterator for IntoIter<T>
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impl<'a, I> ExactSizeIterator for Splice<'a, I> where
I: Iterator,
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I: Iterator,
impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V> where
K: 'a,
V: 'a,
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K: 'a,
V: 'a,
impl<T> ExactSizeIterator for IntoIter<T>
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impl<K, V> ExactSizeIterator for IntoIter<K, V>
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impl<'a, T> ExactSizeIterator for Drain<'a, T> where
T: 'a,
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T: 'a,
impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<T> ExactSizeIterator for IntoIter<T>
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impl<I> ExactSizeIterator for Box<I> where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<T> ExactSizeIterator for IntoIter<T>
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impl<'a, T> ExactSizeIterator for IterMut<'a, T>
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impl<T> ExactSizeIterator for IntoIter<T>
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impl<'a, T> ExactSizeIterator for Drain<'a, T>
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impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>
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impl<'a, T> ExactSizeIterator for IterMut<'a, T>
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impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V> where
K: 'a,
V: 'a,
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K: 'a,
V: 'a,
impl<'a, T> ExactSizeIterator for Drain<'a, T> where
T: 'a,
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T: 'a,
impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<T> ExactSizeIterator for IntoIter<T> where
T: Send + ?Sized,
T: Send + ?Sized,
impl<'a, T> ExactSizeIterator for IterMut<'a, T> where
T: 'a + Send + ?Sized,
T: 'a + Send + ?Sized,
impl<'a, K> ExactSizeIterator for Drain<'a, K>
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impl ExactSizeIterator for EscapeDefault
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impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V>
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impl<'a, K> ExactSizeIterator for Iter<'a, K>
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impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>
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impl<K, V> ExactSizeIterator for IntoIter<K, V>
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impl<'a, K, V> ExactSizeIterator for ValuesMut<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>
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impl<K> ExactSizeIterator for IntoIter<K>
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impl ExactSizeIterator for ArgsOs
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impl<'a, K, V> ExactSizeIterator for Drain<'a, K, V>
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impl ExactSizeIterator for Args
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impl<'a> ExactSizeIterator for Values<'a>
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impl<'a, K, V> ExactSizeIterator for Entries<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Entries<'a, K, V>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>
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impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>
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impl<'a, T> ExactSizeIterator for Iter<'a, T>
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impl<'a, K, V> ExactSizeIterator for IterMut<'a, K, V>
impl<K, V> ExactSizeIterator for IntoIter<K, V>
impl<'a, K, V> ExactSizeIterator for Iter<'a, K, V>
impl<'a, K, V> ExactSizeIterator for Keys<'a, K, V>
impl<'a, K, V> ExactSizeIterator for Values<'a, K, V>
impl<A> ExactSizeIterator for IntoIter<A> where
A: Array,
A: Array,
impl<'a, T> ExactSizeIterator for Drain<'a, T>
impl<T> ExactSizeIterator for Iter<T> where
T: Buf,
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T: Buf,
Implementors
impl<I> ExactSizeIterator for StepBy<I> where
I: ExactSizeIterator,impl<I> ExactSizeIterator for Enumerate<I> where
I: ExactSizeIterator,impl<I> ExactSizeIterator for Take<I> where
I: ExactSizeIterator,impl<I, F> ExactSizeIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item) -> (),
I: ExactSizeIterator,impl<B, I, F> ExactSizeIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: ExactSizeIterator,impl<I> ExactSizeIterator for Fuse<I> where
I: ExactSizeIterator,impl<A, B> ExactSizeIterator for stdcli::prelude::itertools::__std_iter::Zip<A, B> where
A: ExactSizeIterator,
B: ExactSizeIterator,impl<T> ExactSizeIterator for Empty<T>
impl<T> ExactSizeIterator for Once<T>
impl<'a, I, T> ExactSizeIterator for Cloned<I> where
I: ExactSizeIterator<Item = &'a T>,
T: 'a + Clone,impl<I> ExactSizeIterator for Rev<I> where
I: ExactSizeIterator + DoubleEndedIterator,impl<I> ExactSizeIterator for Peekable<I> where
I: ExactSizeIterator,impl<I> ExactSizeIterator for Skip<I> where
I: ExactSizeIterator,impl<L, R> ExactSizeIterator for Either<L, R> where
L: ExactSizeIterator,
R: ExactSizeIterator<Item = <L as Iterator>::Item>,impl<'a> ExactSizeIterator for stdcli::prelude::serde_json::map::Iter<'a>
impl<'a> ExactSizeIterator for stdcli::prelude::serde_json::map::IterMut<'a>
impl<'a> ExactSizeIterator for stdcli::prelude::serde_json::map::Keys<'a>
impl ExactSizeIterator for stdcli::prelude::serde_json::map::IntoIter
impl<'a> ExactSizeIterator for stdcli::prelude::serde_json::map::Values<'a>
impl<A, B, C, D, E, F, G, H> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C, D, E, F, G, H)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,
D: ExactSizeIterator,
E: ExactSizeIterator,
F: ExactSizeIterator,
G: ExactSizeIterator,
H: ExactSizeIterator,impl<I> ExactSizeIterator for WithPosition<I> where
I: ExactSizeIterator,impl<A, B, C, D, E, F> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C, D, E, F)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,
D: ExactSizeIterator,
E: ExactSizeIterator,
F: ExactSizeIterator,impl<A, B> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B)> where
A: ExactSizeIterator,
B: ExactSizeIterator,impl<A, B, C, D, E> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C, D, E)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,
D: ExactSizeIterator,
E: ExactSizeIterator,impl<A> ExactSizeIterator for RepeatN<A> where
A: Clone,impl<I, J> ExactSizeIterator for ZipEq<I, J> where
I: ExactSizeIterator,
J: ExactSizeIterator,impl<I> ExactSizeIterator for Step<I> where
I: ExactSizeIterator,impl<I, F> ExactSizeIterator for Update<I, F> where
F: FnMut(&mut <I as Iterator>::Item) -> (),
I: ExactSizeIterator,impl<I> ExactSizeIterator for MultiPeek<I> where
I: ExactSizeIterator,impl<A, B, C, D> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C, D)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,
D: ExactSizeIterator,impl<I, F> ExactSizeIterator for PadUsing<I, F> where
F: FnMut(usize) -> <I as Iterator>::Item,
I: ExactSizeIterator,impl<A> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A,)> where
A: ExactSizeIterator,impl<I> ExactSizeIterator for Tee<I> where
I: ExactSizeIterator,
<I as Iterator>::Item: Clone,impl<A, B, C, D, E, F, G> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C, D, E, F, G)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,
D: ExactSizeIterator,
E: ExactSizeIterator,
F: ExactSizeIterator,
G: ExactSizeIterator,impl<A, B, C> ExactSizeIterator for stdcli::prelude::itertools::Zip<(A, B, C)> where
A: ExactSizeIterator,
B: ExactSizeIterator,
C: ExactSizeIterator,impl<T> ExactSizeIterator for TupleBuffer<T> where
T: TupleCollect,impl<T, U> ExactSizeIterator for ZipLongest<T, U> where
T: ExactSizeIterator,
U: ExactSizeIterator,