Trait nom::lib::std::prelude::v1::v1::ExactSizeIterator 1.0.0[−][src]
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 = 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 ArgsOs
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impl ExactSizeIterator for ArgsOs
impl ExactSizeIterator for Args
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impl ExactSizeIterator for Args
impl ExactSizeIterator for EscapeUnicode
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impl ExactSizeIterator for EscapeUnicode
impl ExactSizeIterator for EscapeDefault
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impl ExactSizeIterator for EscapeDefault
impl ExactSizeIterator for EscapeDefault
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impl ExactSizeIterator for EscapeDefault
impl<'a, I> ExactSizeIterator for &'a mut I where
I: ExactSizeIterator + ?Sized,
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impl<'a, I> ExactSizeIterator for &'a mut I where
I: ExactSizeIterator + ?Sized,
impl ExactSizeIterator for EscapeDebug
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impl ExactSizeIterator for EscapeDebug
impl<T> ExactSizeIterator for IntoIter<T> where
T: Send + ?Sized,
impl<T> ExactSizeIterator for IntoIter<T> where
T: Send + ?Sized,
impl<'a, T> ExactSizeIterator for IterMut<'a, T> where
T: 'a + Send + ?Sized,
impl<'a, T> ExactSizeIterator for IterMut<'a, T> where
T: 'a + Send + ?Sized,
Implementors
impl<K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IntoIter<K, V>
impl<'a, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Drain<'a, K>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::IterMut<'a, K, V>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Values<'a, K, V>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Keys<'a, K, V>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Drain<'a, K, V>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::ValuesMut<'a, K, V>
impl<'a, K> ExactSizeIterator for nom::lib::std::collections::hash_set::Iter<'a, K>
impl<K> ExactSizeIterator for nom::lib::std::collections::hash_set::IntoIter<K>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::hash_map::Iter<'a, K, V>
impl ExactSizeIterator for Range<usize>
impl<'a, T> ExactSizeIterator for ExactChunks<'a, T>
impl ExactSizeIterator for Range<i8>
impl<'a, T> ExactSizeIterator for nom::lib::std::slice::Iter<'a, T>
impl<I> ExactSizeIterator for Peekable<I> where
I: ExactSizeIterator,impl<'a, A> ExactSizeIterator for nom::lib::std::option::Iter<'a, A>
impl ExactSizeIterator for Range<u8>
impl<I, F> ExactSizeIterator for Inspect<I, F> where
F: FnMut(&<I as Iterator>::Item),
I: ExactSizeIterator,impl<I> ExactSizeIterator for Skip<I> where
I: ExactSizeIterator,impl ExactSizeIterator for RangeInclusive<i16>
impl ExactSizeIterator for RangeInclusive<u8>
impl<T> ExactSizeIterator for Empty<T>
impl ExactSizeIterator for RangeInclusive<i8>
impl<'a, T> ExactSizeIterator for Windows<'a, T>
impl<'a, T> ExactSizeIterator for ExactChunksMut<'a, T>
impl<'a, T> ExactSizeIterator for Chunks<'a, T>
impl ExactSizeIterator for Range<isize>
impl<'a> ExactSizeIterator for Bytes<'a>
impl<B, I, F> ExactSizeIterator for Map<I, F> where
F: FnMut(<I as Iterator>::Item) -> B,
I: ExactSizeIterator,impl<T> ExactSizeIterator for nom::lib::std::result::IntoIter<T>
impl<'a, A> ExactSizeIterator for nom::lib::std::option::IterMut<'a, A>
impl<I> ExactSizeIterator for Enumerate<I> where
I: ExactSizeIterator,impl<'a, T> ExactSizeIterator for nom::lib::std::result::Iter<'a, T>
impl<T> ExactSizeIterator for Once<T>
impl ExactSizeIterator for Range<i16>
impl ExactSizeIterator for Range<u32>
impl<A, B> ExactSizeIterator for Zip<A, B> where
A: ExactSizeIterator,
B: ExactSizeIterator,impl<I> ExactSizeIterator for StepBy<I> where
I: ExactSizeIterator,impl<'a, I, T> ExactSizeIterator for Cloned<I> where
I: ExactSizeIterator<Item = &'a T>,
T: 'a + Clone,impl ExactSizeIterator for Range<i32>
impl<'a, T> ExactSizeIterator for ChunksMut<'a, T>
impl<I> ExactSizeIterator for Rev<I> where
I: ExactSizeIterator + DoubleEndedIterator,impl<I> ExactSizeIterator for Take<I> where
I: ExactSizeIterator,impl ExactSizeIterator for RangeInclusive<u16>
impl ExactSizeIterator for Range<u16>
impl<A> ExactSizeIterator for nom::lib::std::option::IntoIter<A>
impl<'a, T> ExactSizeIterator for nom::lib::std::result::IterMut<'a, T>
impl<'a, T> ExactSizeIterator for nom::lib::std::slice::IterMut<'a, T>
impl<I> ExactSizeIterator for Fuse<I> where
I: ExactSizeIterator,impl<K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IntoIter<K, V>
impl<I> ExactSizeIterator for Box<I> where
I: ExactSizeIterator + ?Sized,impl<'a, T> ExactSizeIterator for nom::lib::std::collections::linked_list::IterMut<'a, T>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Keys<'a, K, V>
impl<T> ExactSizeIterator for nom::lib::std::collections::linked_list::IntoIter<T>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Iter<'a, K, V> where
K: 'a,
V: 'a,impl<'a, T> ExactSizeIterator for nom::lib::std::collections::btree_set::Iter<'a, T>
impl<'a, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Iter<'a, T>
impl<'a, I> ExactSizeIterator for Splice<'a, I> where
I: Iterator,impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::IterMut<'a, K, V> where
K: 'a,
V: 'a,impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::Values<'a, K, V>
impl<T> ExactSizeIterator for nom::lib::std::collections::btree_set::IntoIter<T>
impl<T> ExactSizeIterator for nom::lib::std::vec::IntoIter<T>
impl<T> ExactSizeIterator for nom::lib::std::collections::vec_deque::IntoIter<T>
impl<'a, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Iter<'a, T>
impl<'a, K, V> ExactSizeIterator for nom::lib::std::collections::btree_map::ValuesMut<'a, K, V>
impl<'a, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::IterMut<'a, T>
impl<'a, T> ExactSizeIterator for nom::lib::std::collections::binary_heap::Drain<'a, T> where
T: 'a,impl<T> ExactSizeIterator for nom::lib::std::collections::binary_heap::IntoIter<T>
impl<'a, T> ExactSizeIterator for nom::lib::std::vec::Drain<'a, T>
impl<'a, T> ExactSizeIterator for nom::lib::std::collections::vec_deque::Drain<'a, T> where
T: 'a,impl<'a, T> ExactSizeIterator for nom::lib::std::collections::linked_list::Iter<'a, T>