1.0.0[−][src]Trait kai::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());
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<'_, K, V> ExactSizeIterator for Values<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K, V> ExactSizeIterator for IntoIter<K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K> ExactSizeIterator for Iter<'_, K>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for ArgsOs
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impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Drain<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Args
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impl<K> ExactSizeIterator for IntoIter<K>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K> ExactSizeIterator for Drain<'_, K>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for EscapeDebug
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'a, T> ExactSizeIterator for RChunksExact<'a, T>
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impl<'_, T> ExactSizeIterator for RChunks<'_, T>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for IterMut<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, I> ExactSizeIterator for &'_ mut I where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<T> ExactSizeIterator for IntoIter<T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for ToUppercase
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Iter<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for EscapeDefault
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for ChunksExact<'_, T>
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impl<'_, T> ExactSizeIterator for Windows<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for IterMut<'_, T>
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impl<'_, A> ExactSizeIterator for Iter<'_, A>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Chunks<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for EscapeUnicode
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Iter<'_, T>
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impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, T>
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impl<'_> ExactSizeIterator for Bytes<'_>
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impl ExactSizeIterator for ToLowercase
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, A> ExactSizeIterator for IterMut<'_, A>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for RChunksMut<'_, T>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for EscapeDefault
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<A> ExactSizeIterator for IntoIter<A>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for ChunksExactMut<'_, T>
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impl<'_, T> ExactSizeIterator for Iter<'_, T>
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impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for IterMut<'_, T>
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impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K, V> ExactSizeIterator for IntoIter<K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Iter<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for IntoIter<T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for IntoIter<T>
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impl<'_, T> ExactSizeIterator for Iter<'_, T>
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impl<T> ExactSizeIterator for IntoIter<T>
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impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Drain<'_, T>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Drain<'_, T>
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impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Iter<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for IterMut<'_, T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for IntoIter<T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Drain<'_, T>
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impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, I> ExactSizeIterator for Splice<'_, I> where
I: Iterator,
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I: Iterator,
fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<I> ExactSizeIterator for Box<I> where
I: ExactSizeIterator + ?Sized,
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I: ExactSizeIterator + ?Sized,
impl<'_, K, V> ExactSizeIterator for Keys<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Drain<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K> ExactSizeIterator for Drain<'_, K>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Values<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K> ExactSizeIterator for IntoIter<K>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for ValuesMut<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for IterMut<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K, V> ExactSizeIterator for IntoIter<K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'a, K> ExactSizeIterator for Iter<'a, K>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for Iter<'_, K, V>
fn len(&self) -> usize
fn is_empty(&self) -> bool
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exact_size_is_empty
)Implementors
impl ExactSizeIterator for Range<i16>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<i32>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<i8>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<isize>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u16>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u32>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u8>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<usize>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<i16>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<i8>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<u16>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<u8>
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fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)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, B> ExactSizeIterator for Zip<A, B> where
A: ExactSizeIterator,
B: ExactSizeIterator,
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A: ExactSizeIterator,
B: ExactSizeIterator,
fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<A, F> ExactSizeIterator for OnceWith<F> where
F: FnOnce() -> A,
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F: FnOnce() -> A,
fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)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,
fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)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,
fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<I> ExactSizeIterator for StepBy<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
fn len(&self) -> usize
1.0.0[src]
fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<I> ExactSizeIterator for Take<I> where
I: ExactSizeIterator,
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I: ExactSizeIterator,
fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)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,
impl<T> ExactSizeIterator for Empty<T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for Once<T>
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fn len(&self) -> usize
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fn is_empty(&self) -> bool
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exact_size_is_empty
)