# 1.0.0[−][src]Struct std::collections::btree_map::VacantEntry

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

A view into a vacant entry in a `BTreeMap`. It is part of the `Entry` enum.

## Methods

### `impl<'a, K, V> VacantEntry<'a, K, V> where
K: Ord,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`pub fn key(&self) -> &K`
1.10.0
[src]

Gets a reference to the key that would be used when inserting a value through the VacantEntry.

# Examples

    use std::collections::BTreeMap;

    let mut map: BTreeMap<&str, usize> = BTreeMap::new();
    assert_eq!(map.entry("poneyland").key(), &"poneyland");Run

#### `pub fn into_key(self) -> K`
1.12.0
[src]

Take ownership of the key.

# Examples

    use std::collections::BTreeMap;
    use std::collections::btree_map::Entry;

    let mut map: BTreeMap<&str, usize> = BTreeMap::new();

    if let Entry::Vacant(v) = map.entry("poneyland") {
        v.into_key();
    }Run

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`pub fn insert(self, value: V) -> &'a mut V`[src]

Sets the value of the entry with the `VacantEntry`'s key, and returns a mutable reference to it.

# Examples

    use std::collections::BTreeMap;

    let mut count: BTreeMap<&str, usize> = BTreeMap::new();

    // count the number of occurrences of letters in the vec
    for x in vec!["a","b","a","c","a","b"] {
        *count.entry(x).or_insert(0) += 1;
    }

    assert_eq!(count["a"], 3);Run

## Trait Implementations

### `impl<'a, K, V> Debug for VacantEntry<'a, K, V> where
K: 'a + Ord + Debug,
V: 'a,`
1.12.0
[src]

#### `fn fmt(&self, f: &mut Formatter) -> Result<(), Error>`[src]

Formats the value using the given formatter. Read more

## Auto Trait Implementations

### `impl<'a, K, V> Send for VacantEntry<'a, K, V> where
K: Send,
V: Send,`

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

## Blanket Implementations

### `impl<T, U> TryFrom for T where
T: From<U>,` [src]

#### `type Error = !`

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

#### `fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

### `impl<T> From for T`[src]

#### `fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> TryInto for T where
U: TryFrom<T>,` [src]

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

🔬 This is a nightly-only experimental API. (`try_from` #33417)

The type returned in the event of a conversion error.

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

🔬 This is a nightly-only experimental API. (`try_from` #33417)

Performs the conversion.

### `impl<T, U> Into for T where
U: From<T>,` [src]

#### `fn into(self) -> U`[src]

Performs the conversion.

### `impl<T> Borrow for T where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`fn borrow(&self) -> &T`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut for T where
T: ?Sized,` [src]

####
ⓘImportant traits for &'_ mut I

### Important traits for &'_ mut I

`impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<'a, R: Read + ?Sized> Read for &'a mut Rimpl<'a, W: Write + ?Sized> Write for &'a mut W`
`fn borrow_mut(&mut self) -> &mut T`[src]

Mutably borrows from an owned value. Read more

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `fn get_type_id(&self) -> TypeId`[src]

🔬 This is a nightly-only experimental API. (`get_type_id` #27745)

this method will likely be replaced by an associated static

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

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