# Struct alloc::collections::btree_map::Cursor

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    pub struct Cursor<'a, K: 'a, V: 'a> { /* private fields */ }

🔬This is a nightly-only experimental API. (`btree_cursors` #107540)
Expand description

A cursor over a `BTreeMap`.

A `Cursor` is like an iterator, except that it can freely seek back-and-forth.

Cursors always point to a gap between two elements in the map, and can operate on the two immediately adjacent elements.

A `Cursor` is created with the `BTreeMap::lower_bound` and `BTreeMap::upper_bound` methods.

## Implementations§

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### impl<'a, K, V> Cursor<'a, K, V>

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

🔬This is a nightly-only experimental API. (`btree_cursors` #107540)

Advances the cursor to the next gap, returning the key and value of the element that it moved over.

If the cursor is already at the end of the map then `None` is returned and the cursor is not moved.

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#### pub fn prev(&mut self) -> Option<(&'a K, &'a V)>

🔬This is a nightly-only experimental API. (`btree_cursors` #107540)

Advances the cursor to the previous gap, returning the key and value of the element that it moved over.

If the cursor is already at the start of the map then `None` is returned and the cursor is not moved.

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#### pub fn peek_next(&self) -> Option<(&'a K, &'a V)>

🔬This is a nightly-only experimental API. (`btree_cursors` #107540)

Returns a reference to the the key and value of the next element without moving the cursor.

If the cursor is at the end of the map then `None` is returned

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#### pub fn peek_prev(&self) -> Option<(&'a K, &'a V)>

🔬This is a nightly-only experimental API. (`btree_cursors` #107540)

Returns a reference to the the key and value of the previous element without moving the cursor.

If the cursor is at the start of the map then `None` is returned.

## Trait Implementations§

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

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

Formats the value using the given formatter. Read more

## Auto Trait Implementations§

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### impl<'a, K, V> RefUnwindSafe for Cursor<'a, K, V>
where K: RefUnwindSafe, V: RefUnwindSafe,

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

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

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

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### impl<'a, K, V> UnwindSafe for Cursor<'a, K, V>
where K: RefUnwindSafe, V: RefUnwindSafe,

## Blanket Implementations§

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

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

Returns the argument unchanged.

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

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

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

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

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#### type Owned = T

The resulting type after obtaining ownership.
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#### fn to_owned(&self) -> T

Creates owned data from borrowed data, usually by cloning. Read more
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#### fn clone_into(&self, target: &mut T)

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>,

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#### type Error = Infallible

The type returned in the event of a conversion error.
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#### 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>,

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

The type returned in the event of a conversion error.
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#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.