Struct Slab

Source

pub struct Slab<K: Into<usize> + From<usize>, V> { /* private fields */ }

Expand description

A wrapper for pre-allocated storage for a uniform data type

See module documentation for more details.

Implementations§

Source §

impl<K: Into<usize> + From<usize>, V> Slab<K, V>

Source

pub fn new() -> Slab<K, V>

Construct a new, empty Slab.

The function does not allocate and the returned slab will have no capacity until insert is called or capacity is explicitly reserved.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let slab: Slab<MyIndex, i32> = Slab::new();

Source

pub fn with_capacity(capacity: usize) -> Slab<K, V>

Construct a new, empty Slab with the specified capacity.

The returned slab will be able to store exactly capacity without reallocating. If capacity is 0, the slab will not allocate.

It is important to note that this function does not specify the length of the returned slab, but only the capacity. For an explanation of the difference between length and capacity, see Capacity and reallocation.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab = Slab::<MyIndex, _>::with_capacity(10);

// The slab contains no values, even though it has capacity for more
assert_eq!(slab.len(), 0);

// These are all done without reallocating...
for i in 0..10 {
    slab.insert(i);
}

// ...but this may make the slab reallocate
slab.insert(11);

Source

pub fn capacity(&self) -> usize

Returns the number of values the slab can store without reallocating.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let slab: Slab<MyIndex, i32> = Slab::with_capacity(10);
assert_eq!(slab.capacity(), 10);

Source

pub fn reserve(&mut self, additional: usize)

Reserves capacity for at least additional more values to be stored without allocating.

reserve does nothing if the slab already has sufficient capcity for additional more values. If more capacity is required, a new segment of memory will be allocated and all existing values will be copied into it. As such, if the slab is already very large, a call to reserve can end up being expensive.

The slab may reserve more than additional extra space in order to avoid frequent reallocations. Use reserve_exact instead to guarantee that only the requested space is allocated.

§Panics

Panics if the new capacity overflows usize.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();
slab.insert("hello");
slab.reserve(10);
assert!(slab.capacity() >= 11);

Source

pub fn reserve_exact(&mut self, additional: usize)

Reserves the minimum capacity required to store exactly additional more values.

reserve_exact does nothing if the slab already has sufficient capacity for additional more valus. If more capacity is required, a new segment of memory will be allocated and all existing values will be copied into it. As such, if the slab is already very large, a call to reserve can end up being expensive.

Note that the allocator may give the slab more space than it requests. Therefore capacity can not be relied upon to be precisely minimal. Prefer reserve if future insertions are expected.

§Panics

Panics if the new capacity overflows usize.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();
slab.insert("hello");
slab.reserve_exact(10);
assert!(slab.capacity() >= 11);

Source

pub fn shrink_to_fit(&mut self)

Shrinks the capacity of the slab as much as possible.

It will drop down as close as possible to the length but the allocator may still inform the vector that there is space for a few more elements. Also, since values are not moved, the slab cannot shrink past any stored values.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, i32> = Slab::with_capacity(10);

for i in 0..3 {
    slab.insert(i);
}

assert_eq!(slab.capacity(), 10);
slab.shrink_to_fit();
assert!(slab.capacity() >= 3);

In this case, even though two values are removed, the slab cannot shrink past the last value.

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, i32> = Slab::with_capacity(10);

for i in 0..3 {
    slab.insert(i);
}

slab.remove(0.into());
slab.remove(1.into());

assert_eq!(slab.capacity(), 10);
slab.shrink_to_fit();
assert!(slab.capacity() >= 3);

Source

pub fn clear(&mut self)

Clear the slab of all values

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();

for i in 0..3 {
    slab.insert(i);
}

slab.clear();
assert!(slab.is_empty());

Source

pub fn len(&self) -> usize

Returns the number of stored values

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();

for i in 0..3 {
    slab.insert(i);
}

assert_eq!(3, slab.len());

Source

pub fn is_empty(&self) -> bool

Returns true if no values are stored in the slab

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, usize> = Slab::new();
assert!(slab.is_empty());

slab.insert(1);
assert!(!slab.is_empty());

Source

pub fn iter(&self) -> Iter<'_, K, V> ⓘ

Returns an iterator over the slab

This function should generally be avoided as it is not efficient. Iterators must iterate over every slot in the slab even if it is vaccant. As such, a slab with a capacity of 1 million but only one stored value must still iterate the million slots.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, u32> = Slab::new();

for i in 0..3 {
    slab.insert(i);
}

let mut iterator = slab.iter();

assert_eq!(iterator.next(), Some((0.into(), &0)));
assert_eq!(iterator.next(), Some((1.into(), &1)));
assert_eq!(iterator.next(), Some((2.into(), &2)));
assert_eq!(iterator.next(), None);

Source

pub fn iter_mut(&mut self) -> IterMut<'_, K, V> ⓘ

Returns an iterator that allows modifying each value.

This function should generally be avoided as it is not efficient. Iterators must iterate over every slot in the slab even if it is vaccant. As such, a slab with a capacity of 1 million but only one stored value must still iterate the million slots.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, u32> = Slab::new();

let key1 = slab.insert(0);
let key2 = slab.insert(1);

for (key, val) in slab.iter_mut() {
    if key == key1 {
        *val += 2;
    }
}

assert_eq!(slab[key1], 2);
assert_eq!(slab[key2], 1);

Source

pub fn get(&self, key: K) -> Option<&V>

Returns a reference to the value associated with the given key

If the given key is not associated with a value, then None is returned.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();
let key : MyIndex = slab.insert("hello");

assert_eq!(slab.get(key), Some(&"hello"));
assert_eq!(slab.get(123.into()), None);

Source

pub fn get_mut(&mut self, key: K) -> Option<&mut V>

Returns a mutable reference to the value associated with the given key

If the given key is not associated with a value, then None is returned.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, &'static str> = Slab::new();
let key : MyIndex = slab.insert("hello");

*slab.get_mut(key).unwrap() = "world";

assert_eq!(slab[key], "world");
assert_eq!(slab.get_mut(123.into()), None);

Source

pub unsafe fn get_unchecked(&self, key: K) -> &V

Returns a reference to the value associated with the given key without performing bounds checking.

This function should be used with care.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex,_> = Slab::new();
let key : MyIndex = slab.insert(2);

unsafe {
    assert_eq!(slab.get_unchecked(key), &2);
}

Source

pub unsafe fn get_unchecked_mut(&mut self, key: K) -> &mut V

Returns a mutable reference to the value associated with the given key without performing bounds checking.

This function should be used with care.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab < MyIndex, u16> = Slab::new();
let key = slab.insert(2);

unsafe {
    let val = slab.get_unchecked_mut(key);
    *val = 13;
}

assert_eq!(slab[key], 13);

Source

pub fn insert(&mut self, val: V) -> K

Insert a value in the slab, returning key assigned to the value

The returned key can later be used to retrieve or remove the value using indexed lookup and remove. Additional capacity is allocated if needed. See Capacity and reallocation.

§Panics

Panics if the number of elements in the vector overflows a usize.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();
let key : MyIndex = slab.insert("hello");
assert_eq!(slab[key], "hello");

Source

pub fn vacant_entry(&mut self) -> VacantEntry<'_, K, V>

Returns a handle to a vacant entry allowing for further manipulation.

This function is useful when creating values that must contain their slab key. The returned VaccantEntry reserves a slot in the slab and is able to query the associated key.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab  : Slab<MyIndex, _> = Slab::new();

let hello = {
    let entry = slab.vacant_entry();
    let key : MyIndex  = entry.key();

    entry.insert((key, "hello"));
    key
};

assert_eq!(hello, slab[hello].0);
assert_eq!("hello", slab[hello].1);

Source

pub fn remove(&mut self, key: K) -> V

Removes and returns the value associated with the given key.

The key is then released and may be associated with future stored values.

§Panics

Panics if key is not associated with a value.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex,_> = Slab::new();

let hello : MyIndex = slab.insert("hello");

assert_eq!(slab.remove(hello), "hello");
assert!(!slab.contains(hello));

Source

pub fn try_remove(&mut self, key: K) -> Option<V>

Removes and returns the value associated with the given key, if it exists.

The key is then released and may be associated with future stored values.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex,_> = Slab::new();

let hello : MyIndex = slab.insert("hello");

assert_eq!(slab.try_remove(hello), Some("hello"));
assert_eq!(slab.try_remove(hello), None);

Source

pub fn contains(&self, key: K) -> bool

Returns true if a value is associated with the given key.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex,_> = Slab::new();

let hello : MyIndex = slab.insert("hello");
assert!(slab.contains(hello));

slab.remove(hello);

assert!(!slab.contains(hello));

Source

pub fn retain<F>(&mut self, f: F)
where F: FnMut(K, &mut V) -> bool,

Retain only the elements specified by the predicate.

In other words, remove all elements e such that f(usize, &mut e) returns false. This method operates in place and preserves the key associated with the retained values.

§Examples

#[macro_use] extern crate slab_typesafe;
declare_slab_token!(MyIndex);
let mut slab : Slab<MyIndex, _> = Slab::new();

let k1 : MyIndex = slab.insert(0);
let k2 : MyIndex = slab.insert(1);
let k3 : MyIndex = slab.insert(2);

slab.retain(|key, val| key == k1 || *val == 1);

assert!(slab.contains(k1));
assert!(slab.contains(k2));
assert!(!slab.contains(k3));

assert_eq!(2, slab.len());