Keys in alloc::collections::btree_map - Rust
Description: An iterator over the keys of a `BTreeMap`.
Keywords: rust, rustlang, rust-lang, Keys

# Struct alloc::collections::btree_map::Keys
1.0.0[−][src]

    pub struct Keys<'a, K: 'a, V: 'a> { /* fields omitted */ }

Expand description

An iterator over the keys of a `BTreeMap`.

This `struct` is created by the `keys` method on `BTreeMap`. See its documentation for more.

## Trait Implementations

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### impl<K, V> Clone for Keys<'_, K, V>

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#### fn clone(&self) -> Self

Returns a copy of the value. Read more

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#### fn clone_from(&mut self, source: &Self)

Performs copy-assignment from `source`. Read more

1.17.0[src]

### impl<K: Debug, V> Debug for Keys<'_, K, V>

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#### fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter. Read more

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### impl<'a, K, V> DoubleEndedIterator for Keys<'a, K, V>

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#### fn next_back(&mut self) -> Option<&'a K>

Removes and returns an element from the end of the iterator. Read more

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#### fn advance_back_by(&mut self, n: usize) -> Result<(), usize>

🔬 This is a nightly-only experimental API. (`iter_advance_by` #77404)

recently added

Advances the iterator from the back by `n` elements. Read more

1.37.0[src]

#### fn nth_back(&mut self, n: usize) -> Option<Self::Item>

Returns the `n`th element from the end of the iterator. Read more

1.27.0[src]

#### fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Output = B>,

This is the reverse version of `Iterator::try_fold()`: it takes elements starting from the back of the iterator. Read more

1.27.0[src]

#### fn rfold<B, F>(self, init: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,

An iterator method that reduces the iterator’s elements to a single, final value, starting from the back. Read more

1.27.0[src]

#### fn rfind<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator from the back that satisfies a predicate. Read more

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### impl<K, V> ExactSizeIterator for Keys<'_, K, V>

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#### fn len(&self) -> usize

Returns the exact length of the iterator. Read more

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#### fn is_empty(&self) -> bool

🔬 This is a nightly-only experimental API. (`exact_size_is_empty` #35428)

Returns `true` if the iterator is empty. Read more

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### impl<'a, K, V> Iterator for Keys<'a, K, V>

#### type Item = &'a K

The type of the elements being iterated over.

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#### fn next(&mut self) -> Option<&'a K>

Advances the iterator and returns the next value. Read more

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#### fn size_hint(&self) -> (usize, Option<usize>)

Returns the bounds on the remaining length of the iterator. Read more

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#### fn last(self) -> Option<&'a K>

Consumes the iterator, returning the last element. Read more

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#### fn min(self) -> Option<&'a K>

Returns the minimum element of an iterator. Read more

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#### fn max(self) -> Option<&'a K>

Returns the maximum element of an iterator. Read more

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#### fn count(self) -> usize

Consumes the iterator, counting the number of iterations and returning it. Read more

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#### fn advance_by(&mut self, n: usize) -> Result<(), usize>

🔬 This is a nightly-only experimental API. (`iter_advance_by` #77404)

recently added

Advances the iterator by `n` elements. Read more

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#### fn nth(&mut self, n: usize) -> Option<Self::Item>

Returns the `n`th element of the iterator. Read more

1.28.0[src]

#### fn step_by(self, step: usize) -> StepBy<Self>

Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more

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#### fn chain<U>(self, other: U) -> Chain<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator<Item = Self::Item>,

Takes two iterators and creates a new iterator over both in sequence. Read more

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#### fn zip<U>(self, other: U) -> Zip<Self, <U as IntoIterator>::IntoIter> where
U: IntoIterator,

‘Zips up’ two iterators into a single iterator of pairs. Read more

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#### fn intersperse(self, separator: Self::Item) -> Intersperse<Self> where
Self::Item: Clone,

🔬 This is a nightly-only experimental API. (`iter_intersperse` #79524)

recently added

Creates a new iterator which places a copy of `separator` between adjacent items of the original iterator. Read more

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#### fn intersperse_with<G>(self, separator: G) -> IntersperseWith<Self, G> where
G: FnMut() -> Self::Item,

🔬 This is a nightly-only experimental API. (`iter_intersperse` #79524)

recently added

Creates a new iterator which places an item generated by `separator` between adjacent items of the original iterator. Read more

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#### fn map<B, F>(self, f: F) -> Map<Self, F> where
F: FnMut(Self::Item) -> B,

Takes a closure and creates an iterator which calls that closure on each element. Read more

1.21.0[src]

#### fn for_each<F>(self, f: F) where
F: FnMut(Self::Item),

Calls a closure on each element of an iterator. Read more

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#### fn filter<P>(self, predicate: P) -> Filter<Self, P> where
P: FnMut(&Self::Item) -> bool,

Creates an iterator which uses a closure to determine if an element should be yielded. Read more

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#### fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where
F: FnMut(Self::Item) -> Option<B>,

Creates an iterator that both filters and maps. Read more

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#### fn enumerate(self) -> Enumerate<Self>

Creates an iterator which gives the current iteration count as well as the next value. Read more

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#### fn peekable(self) -> Peekable<Self>

Creates an iterator which can use the `peek` and `peek_mut` methods to look at the next element of the iterator without consuming it. See their documentation for more information. Read more

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#### fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where
P: FnMut(&Self::Item) -> bool,

Creates an iterator that `skip`s elements based on a predicate. Read more

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#### fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where
P: FnMut(&Self::Item) -> bool,

Creates an iterator that yields elements based on a predicate. Read more

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#### fn map_while<B, P>(self, predicate: P) -> MapWhile<Self, P> where
P: FnMut(Self::Item) -> Option<B>,

🔬 This is a nightly-only experimental API. (`iter_map_while` #68537)

recently added

Creates an iterator that both yields elements based on a predicate and maps. Read more

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#### fn skip(self, n: usize) -> Skip<Self>

Creates an iterator that skips the first `n` elements. Read more

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#### fn take(self, n: usize) -> Take<Self>

Creates an iterator that yields the first `n` elements, or fewer if the underlying iterator ends sooner. Read more

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#### fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where
F: FnMut(&mut St, Self::Item) -> Option<B>,

An iterator adaptor similar to `fold` that holds internal state and produces a new iterator. Read more

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#### fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where
F: FnMut(Self::Item) -> U,
U: IntoIterator,

Creates an iterator that works like map, but flattens nested structure. Read more

1.29.0[src]

#### fn flatten(self) -> Flatten<Self> where
Self::Item: IntoIterator,

Creates an iterator that flattens nested structure. Read more

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#### fn fuse(self) -> Fuse<Self>

Creates an iterator which ends after the first `None`. Read more

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#### fn inspect<F>(self, f: F) -> Inspect<Self, F> where
F: FnMut(&Self::Item),

Does something with each element of an iterator, passing the value on. Read more

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#### fn by_ref(&mut self) -> &mut Self

Borrows an iterator, rather than consuming it. Read more

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#### fn collect<B>(self) -> B where
B: FromIterator<Self::Item>,

Transforms an iterator into a collection. Read more

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#### fn partition<B, F>(self, f: F) -> (B, B) where
F: FnMut(&Self::Item) -> bool,
B: Default + Extend<Self::Item>,

Consumes an iterator, creating two collections from it. Read more

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#### fn partition_in_place<'a, T, P>(self, predicate: P) -> usize where
Self: DoubleEndedIterator<Item = &'a mut T>,
T: 'a,
P: FnMut(&T) -> bool,

🔬 This is a nightly-only experimental API. (`iter_partition_in_place` #62543)

new API

Reorders the elements of this iterator in-place according to the given predicate, such that all those that return `true` precede all those that return `false`. Returns the number of `true` elements found. Read more

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#### fn is_partitioned<P>(self, predicate: P) -> bool where
P: FnMut(Self::Item) -> bool,

🔬 This is a nightly-only experimental API. (`iter_is_partitioned` #62544)

new API

Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return `true` precede all those that return `false`. Read more

1.27.0[src]

#### fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where
F: FnMut(B, Self::Item) -> R,
R: Try<Output = B>,

An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more

1.27.0[src]

#### fn try_for_each<F, R>(&mut self, f: F) -> R where
F: FnMut(Self::Item) -> R,
R: Try<Output = ()>,

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error. Read more

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#### fn fold<B, F>(self, init: B, f: F) -> B where
F: FnMut(B, Self::Item) -> B,

Folds every element into an accumulator by applying an operation, returning the final result. Read more

1.51.0[src]

#### fn reduce<F>(self, f: F) -> Option<Self::Item> where
F: FnMut(Self::Item, Self::Item) -> Self::Item,

Reduces the elements to a single one, by repeatedly applying a reducing operation. Read more

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#### fn all<F>(&mut self, f: F) -> bool where
F: FnMut(Self::Item) -> bool,

Tests if every element of the iterator matches a predicate. Read more

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#### fn any<F>(&mut self, f: F) -> bool where
F: FnMut(Self::Item) -> bool,

Tests if any element of the iterator matches a predicate. Read more

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#### fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where
P: FnMut(&Self::Item) -> bool,

Searches for an element of an iterator that satisfies a predicate. Read more

1.30.0[src]

#### fn find_map<B, F>(&mut self, f: F) -> Option<B> where
F: FnMut(Self::Item) -> Option<B>,

Applies function to the elements of iterator and returns the first non-none result. Read more

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#### fn try_find<F, R, E>(&mut self, f: F) -> Result<Option<Self::Item>, E> where
F: FnMut(&Self::Item) -> R,
R: Try<Output = bool, Residual = Result<Infallible, E>> + Try,

🔬 This is a nightly-only experimental API. (`try_find` #63178)

new API

Applies function to the elements of iterator and returns the first true result or the first error. Read more

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#### fn position<P>(&mut self, predicate: P) -> Option<usize> where
P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator, returning its index. Read more

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#### fn rposition<P>(&mut self, predicate: P) -> Option<usize> where
Self: ExactSizeIterator + DoubleEndedIterator,
P: FnMut(Self::Item) -> bool,

Searches for an element in an iterator from the right, returning its index. Read more

1.6.0[src]

#### fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where
F: FnMut(&Self::Item) -> B,
B: Ord,

Returns the element that gives the maximum value from the specified function. Read more

1.15.0[src]

#### fn max_by<F>(self, compare: F) -> Option<Self::Item> where
F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the maximum value with respect to the specified comparison function. Read more

1.6.0[src]

#### fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where
F: FnMut(&Self::Item) -> B,
B: Ord,

Returns the element that gives the minimum value from the specified function. Read more

1.15.0[src]

#### fn min_by<F>(self, compare: F) -> Option<Self::Item> where
F: FnMut(&Self::Item, &Self::Item) -> Ordering,

Returns the element that gives the minimum value with respect to the specified comparison function. Read more

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#### fn rev(self) -> Rev<Self> where
Self: DoubleEndedIterator,

Reverses an iterator’s direction. Read more

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#### fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where
Self: Iterator<Item = (A, B)>,
FromA: Default + Extend<A>,
FromB: Default + Extend<B>,

Converts an iterator of pairs into a pair of containers. Read more

1.36.0[src]

#### fn copied<'a, T>(self) -> Copied<Self> where
Self: Iterator<Item = &'a T>,
T: 'a + Copy,

Creates an iterator which copies all of its elements. Read more

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#### fn cloned<'a, T>(self) -> Cloned<Self> where
Self: Iterator<Item = &'a T>,
T: 'a + Clone,

Creates an iterator which `clone`s all of its elements. Read more

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#### fn cycle(self) -> Cycle<Self> where
Self: Clone,

Repeats an iterator endlessly. Read more

1.11.0[src]

#### fn sum<S>(self) -> S where
S: Sum<Self::Item>,

Sums the elements of an iterator. Read more

1.11.0[src]

#### fn product<P>(self) -> P where
P: Product<Self::Item>,

Iterates over the entire iterator, multiplying all the elements Read more

1.5.0[src]

#### fn cmp<I>(self, other: I) -> Ordering where
I: IntoIterator<Item = Self::Item>,
Self::Item: Ord,

Lexicographically compares the elements of this `Iterator` with those of another. Read more

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#### fn cmp_by<I, F>(self, other: I, cmp: F) -> Ordering where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Ordering,

🔬 This is a nightly-only experimental API. (`iter_order_by` #64295)

Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function. Read more

1.5.0[src]

#### fn partial_cmp<I>(self, other: I) -> Option<Ordering> where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,

Lexicographically compares the elements of this `Iterator` with those of another. Read more

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#### fn partial_cmp_by<I, F>(self, other: I, partial_cmp: F) -> Option<Ordering> where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> Option<Ordering>,

🔬 This is a nightly-only experimental API. (`iter_order_by` #64295)

Lexicographically compares the elements of this `Iterator` with those of another with respect to the specified comparison function. Read more

1.5.0[src]

#### fn eq<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are equal to those of another. Read more

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#### fn eq_by<I, F>(self, other: I, eq: F) -> bool where
I: IntoIterator,
F: FnMut(Self::Item, <I as IntoIterator>::Item) -> bool,

🔬 This is a nightly-only experimental API. (`iter_order_by` #64295)

Determines if the elements of this `Iterator` are equal to those of another with respect to the specified equality function. Read more

1.5.0[src]

#### fn ne<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialEq<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are unequal to those of another. Read more

1.5.0[src]

#### fn lt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are lexicographically less than those of another. Read more

1.5.0[src]

#### fn le<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are lexicographically less or equal to those of another. Read more

1.5.0[src]

#### fn gt<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are lexicographically greater than those of another. Read more

1.5.0[src]

#### fn ge<I>(self, other: I) -> bool where
I: IntoIterator,
Self::Item: PartialOrd<<I as IntoIterator>::Item>,

Determines if the elements of this `Iterator` are lexicographically greater than or equal to those of another. Read more

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#### fn is_sorted(self) -> bool where
Self::Item: PartialOrd<Self::Item>,

🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

Checks if the elements of this iterator are sorted. Read more

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#### fn is_sorted_by<F>(self, compare: F) -> bool where
F: FnMut(&Self::Item, &Self::Item) -> Option<Ordering>,

🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

Checks if the elements of this iterator are sorted using the given comparator function. Read more

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#### fn is_sorted_by_key<F, K>(self, f: F) -> bool where
F: FnMut(Self::Item) -> K,
K: PartialOrd<K>,

🔬 This is a nightly-only experimental API. (`is_sorted` #53485)

new API

Checks if the elements of this iterator are sorted using the given key extraction function. Read more

1.26.0[src]

### impl<K, V> FusedIterator for Keys<'_, K, V>

## Auto Trait Implementations

### impl<'a, K, V> Send for Keys<'a, K, V> where
K: Sync,
V: Sync,

### impl<'a, K, V> Sync for Keys<'a, K, V> where
K: Sync,
V: Sync,

### impl<'a, K, V> Unpin for Keys<'a, K, V>

## Blanket Implementations

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### impl<T> Any for T where
T: 'static + ?Sized,

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#### pub fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more

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### impl<T> Borrow<T> for T where
T: ?Sized,

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#### pub fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more

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### impl<T> BorrowMut<T> for T where
T: ?Sized,

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#### pub fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more

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### impl<T> From<T> for T

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#### pub fn from(t: T) -> T

Performs the conversion.

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### impl<T, U> Into<U> for T where
U: From<T>,

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#### pub fn into(self) -> U

Performs the conversion.

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### impl<I> IntoIterator for I where
I: Iterator,

#### type Item = <I as Iterator>::Item

The type of the elements being iterated over.

#### type IntoIter = I

Which kind of iterator are we turning this into?

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#### pub fn into_iter(self) -> I

Creates an iterator from a value. Read more

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### impl<T> ToOwned for T where
T: Clone,

#### type Owned = T

The resulting type after obtaining ownership.

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#### pub fn to_owned(&Self) -> T

Creates owned data from borrowed data, usually by cloning. Read more

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#### pub fn clone_into(&Self, &mut T)

🔬 This is a nightly-only experimental API. (`toowned_clone_into` #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

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### impl<T, U> TryFrom<U> for T where
U: Into<T>,

#### type Error = Infallible

The type returned in the event of a conversion error.

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#### pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.

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### impl<T, U> TryInto<U> for T where
U: TryFrom<T>,

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.

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#### pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.