1.0.0[−][src]Trait nom::lib::std::prelude::v1::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
default 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());
default 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 ExactSizeIterator for Args
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impl ExactSizeIterator for ArgsOs
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impl ExactSizeIterator for EscapeUnicode
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for ToUppercase
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default fn len(&self) -> usize
1.0.0[src]
default 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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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for EscapeDebug
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default fn len(&self) -> usize
1.0.0[src]
default 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 ExactSizeIterator for EscapeDefault
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for ToLowercase
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'a, T> ExactSizeIterator for IterMut<'a, T> where
T: 'a + Send + ?Sized,
T: 'a + Send + ?Sized,
default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for IntoIter<T> where
T: Send + ?Sized,
T: Send + ?Sized,
default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)Implementors
impl ExactSizeIterator for Range<isize>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<usize>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<i16>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<i32>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<i8>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u16>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u32>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for Range<u8>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<i16>
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<i8>
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<u16>
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl ExactSizeIterator for RangeInclusive<u8>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_> ExactSizeIterator for Bytes<'_>
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impl<'_, A> ExactSizeIterator for nom::lib::std::option::IterMut<'_, A>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, A> ExactSizeIterator for nom::lib::std::option::Iter<'_, A>
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default fn len(&self) -> usize
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default 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,
default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Iter<'_, K>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Drain<'_, K>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IterMut<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::ValuesMut<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Keys<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Values<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Drain<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Iter<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Keys<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Values<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IterMut<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Iter<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::ValuesMut<'_, K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for RChunksExactMut<'_, 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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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for ChunksMut<'_, T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for RChunksMut<'_, T>
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for nom::lib::std::result::Iter<'_, T>
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default fn len(&self) -> usize
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default 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 nom::lib::std::slice::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::result::IterMut<'_, T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Chunks<'_, T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for Windows<'_, T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for nom::lib::std::slice::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::vec::Drain<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::collections::btree_set::Iter<'_, T>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Drain<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::collections::linked_list::Iter<'_, T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Iter<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Drain<'_, T>
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default fn len(&self) -> usize
1.0.0[src]
default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<'_, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::IterMut<'_, T>
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impl<'_, T> ExactSizeIterator for nom::lib::std::collections::linked_list::IterMut<'_, T>
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default fn len(&self) -> usize
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default 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, T> ExactSizeIterator for RChunksExact<'a, T>
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impl<A> ExactSizeIterator for nom::lib::std::option::IntoIter<A>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<A, B> ExactSizeIterator for Zip<A, B> where
A: ExactSizeIterator,
B: ExactSizeIterator,
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A: ExactSizeIterator,
B: ExactSizeIterator,
default fn len(&self) -> usize
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default 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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default 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,
default fn len(&self) -> usize
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default 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,
default fn len(&self) -> usize
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default 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,
default fn len(&self) -> usize
1.0.0[src]
default 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,
default fn len(&self) -> usize
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default 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<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<K> ExactSizeIterator for nom::lib::std::collections::hash_set::IntoIter<K>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IntoIter<K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IntoIter<K, V>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for nom::lib::std::result::IntoIter<T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for Empty<T>
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fn len(&self) -> usize
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default 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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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for nom::lib::std::collections::binary_heap::IntoIter<T>
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impl<T> ExactSizeIterator for nom::lib::std::collections::btree_set::IntoIter<T>
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fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)impl<T> ExactSizeIterator for nom::lib::std::collections::linked_list::IntoIter<T>
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default fn len(&self) -> usize
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default fn is_empty(&self) -> bool
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exact_size_is_empty
)