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## CursorMutKey

# Struct CursorMutKey

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    pub struct CursorMutKey<'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, and which allows mutating the key of elements.

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

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

A `CursorMutKey` is created from a `CursorMut` with the `CursorMut::with_mutable_key` method.

## §Safety

Since this cursor allows mutating keys, 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.

## Implementations§

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

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#### pub fn next(&mut self) -> Option<(&mut K, &mut 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<(&mut K, &mut 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(&mut self) -> Option<(&mut 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 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(&mut self) -> Option<(&mut 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 without moving the cursor.

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

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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 same location as the `CursorMutKey`.

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

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### impl<'a, K: Ord, V, A: Allocator + Clone> CursorMutKey<'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 key-value pair into the map in the gap that the cursor is currently pointing to.

After the insertion the cursor will be pointing at the gap before the newly inserted element.

##### §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.

Source

#### 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 key-value pair into the map in the gap that the cursor is currently pointing to.

After the insertion the cursor will be pointing at the gap after the newly inserted element.

##### §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.

Source

#### pub fn insert_after( &mut self, key: K, value: V, ) -> Result<(), UnorderedKeyError>

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

Inserts a new key-value pair into the map in the gap that the cursor is currently pointing to.

After the insertion the cursor will be pointing at the gap before the newly inserted element.

If the inserted key is not greater than the key before the cursor (if any), or if it not less than the key after the cursor (if any), then an `UnorderedKeyError` is returned since this would invalidate the `Ord` invariant between the keys of the map.

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#### pub fn insert_before( &mut self, key: K, value: V, ) -> Result<(), UnorderedKeyError>

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

Inserts a new key-value pair into the map in the gap that the cursor is currently pointing to.

After the insertion the cursor will be pointing at the gap after the newly inserted element.

If the inserted key is not greater than the key before the cursor (if any), or if it not less than the key after the cursor (if any), then an `UnorderedKeyError` is returned since this would invalidate the `Ord` invariant between the keys of the map.

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

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

Removes the next element from the `BTreeMap`.

The element that was removed is returned. The cursor position is unchanged (before the removed element).

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

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

Removes the preceding element from the `BTreeMap`.

The element that was removed is returned. The cursor position is unchanged (after the removed element).

## Trait Implementations§

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### impl<K: Debug, V: Debug, A> Debug for CursorMutKey<'_, 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> Freeze for CursorMutKey<'a, K, V, A>

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

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

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

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

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### impl<'a, K, V, A> UnsafeUnpin for CursorMutKey<'a, K, V, A>

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

## 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, 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.