# Struct alloc::collections::btree_map::CursorMut

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    pub struct CursorMut<'a, K: 'a, V: 'a, A = Global> { /* private fields */ }

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

A cursor over a `BTreeMap` with editing operations.

A `Cursor` is like an iterator, except that it can freely seek back-and-forth, and can safely mutate the tree during iteration. This is because the lifetime of its yielded references is tied to its own lifetime, instead of just the underlying tree. This means cursors cannot yield multiple elements at once.

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_mut` and `BTreeMap::upper_bound_mut` methods.

## Implementations§

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### impl<'a, K, V, A> CursorMut<'a, K, V, A>

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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<&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<&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<(&K, &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 value_mut(&mut self) -> Option<&mut V>

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

Returns a mutable 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_mut(&mut self) -> Option<(&K, &mut V)>

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

Returns a reference to the key and mutable 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 unsafe fn key_mut_unchecked(&mut self) -> Option<&mut K>

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

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

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

##### Safety

This can be used to modify the key, but you must ensure that the `BTreeMap` invariants are maintained. Specifically:

- The key must remain unique within the tree.
- The key must remain in sorted order with regards to other elements in the tree.

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

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

Returns a reference to the key and value of 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(&mut self) -> Option<(&K, &mut V)>

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

Returns a reference to the key and value of 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`.

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#### pub fn as_cursor(&self) -> Cursor<'_, K, V>

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

Returns a read-only cursor pointing to the current element.

The lifetime of the returned `Cursor` is bound to that of the `CursorMut`, which means it cannot outlive the `CursorMut` and that the `CursorMut` is frozen for the lifetime of the `Cursor`.

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### impl<'a, K: Ord, V, A: Allocator + Clone> CursorMut<'a, K, V, A>

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#### pub unsafe fn insert_after_unchecked(&mut self, key: K, value: V)

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

Inserts a new element into the `BTreeMap` after the current one.

If the cursor is pointing at the “ghost” non-element then the new element is inserted at the front of the `BTreeMap`.

##### Safety

You must ensure that the `BTreeMap` invariants are maintained. Specifically:

- The key of the newly inserted element must be unique in the tree.
- All keys in the tree must remain in sorted order.

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#### pub unsafe fn insert_before_unchecked(&mut self, key: K, value: V)

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

Inserts a new element into the `BTreeMap` before the current one.

If the cursor is pointing at the “ghost” non-element then the new element is inserted at the end of the `BTreeMap`.

##### Safety

You must ensure that the `BTreeMap` invariants are maintained. Specifically:

- The key of the newly inserted element must be unique in the tree.
- All keys in the tree must remain in sorted order.

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#### pub fn insert_after(&mut self, key: K, value: V)

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

Inserts a new element into the `BTreeMap` after the current one.

If the cursor is pointing at the “ghost” non-element then the new element is inserted at the front of the `BTreeMap`.

##### Panics

This function panics if:

- the given key compares less than or equal to the current element (if any).
- the given key compares greater than or equal to the next element (if any).

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#### pub fn insert_before(&mut self, key: K, value: V)

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

Inserts a new element into the `BTreeMap` before the current one.

If the cursor is pointing at the “ghost” non-element then the new element is inserted at the end of the `BTreeMap`.

##### Panics

This function panics if:

- the given key compares greater than or equal to the current element (if any).
- the given key compares less than or equal to the previous element (if any).

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#### pub fn remove_current(&mut self) -> Option<(K, V)>

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

Removes the current element from the `BTreeMap`.

The element that was removed is returned, and the cursor is moved to point to the next element in the `BTreeMap`.

If the cursor is currently pointing to the “ghost” non-element then no element is removed and `None` is returned. The cursor is not moved in this case.

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#### pub fn remove_current_and_move_back(&mut self) -> Option<(K, V)>

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

Removes the current element from the `BTreeMap`.

The element that was removed is returned, and the cursor is moved to point to the previous element in the `BTreeMap`.

If the cursor is currently pointing to the “ghost” non-element then no element is removed and `None` is returned. The cursor is not moved in this case.

## Trait Implementations§

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

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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, A> RefUnwindSafe for CursorMut<'a, K, V, A>where A: RefUnwindSafe, K: RefUnwindSafe, V: RefUnwindSafe,

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### impl<'a, K, V, A> Send for CursorMut<'a, K, V, A>where A: Send, K: Send, V: Send,

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

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### impl<'a, K, V, A> Unpin for CursorMut<'a, K, V, A>

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### impl<'a, K, V, A = Global> !UnwindSafe for CursorMut<'a, K, V, A>

## 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,

const: unstable · source§

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

Immutably borrows from an owned value. Read more
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### impl<T> BorrowMut<T> for Twhere T: ?Sized,

const: unstable · source§

#### 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

const: unstable · source§

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

Returns the argument unchanged.

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

const: unstable · source§

#### 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, 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.
const: unstable · source§

#### 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.
const: unstable · source§

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

Performs the conversion.