# 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 an element in the tree, and index in a logically circular way. To accommodate this, there is a “ghost” non-element that yields `None` between the last and first elements of the tree.

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 move_next(&mut self)

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

Moves the cursor to the next element of the `BTreeMap`.

If the cursor is pointing to the “ghost” non-element then this will move it to the first element of the `BTreeMap`. If it is pointing to the last element of the `BTreeMap` then this will move it to the “ghost” non-element.

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#### pub fn move_prev(&mut self)

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

Moves the cursor to the previous element of the `BTreeMap`.

If the cursor is pointing to the “ghost” non-element then this will move it to the last element of the `BTreeMap`. If it is pointing to the first element of the `BTreeMap` then this will move it to the “ghost” non-element.

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

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

Returns a reference to the key of the element that the cursor is currently pointing to.

This returns `None` if the cursor is currently pointing to the “ghost” non-element.

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#### pub fn value(&self) -> Option<&'a V>

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

Returns a reference to the value of the element that the cursor is currently pointing to.

This returns `None` if the cursor is currently pointing to the “ghost” non-element.

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

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

Returns a reference to the key and value of the element that the cursor is currently pointing to.

This returns `None` if the cursor is currently pointing to the “ghost” non-element.

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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 next element.

If the cursor is pointing to the “ghost” non-element then this returns the first element of the `BTreeMap`. If it is pointing to the last element of the `BTreeMap` then this returns `None`.

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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 previous element.

If the cursor is pointing to the “ghost” non-element then this returns the last element of the `BTreeMap`. If it is pointing to the first element of the `BTreeMap` then this returns `None`.

## 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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 Twhere 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.