Trait Capacity

pub trait Capacity: Len {
    // Required method
    fn capacity(&self) -> usize;
}

A trait for describing the capacity of a collection.

Because frequently allocating memory can be inefficient, collections often store room for more data than they actually hold. This “extra length” is represented by capacity, stating the maximum length that can be occupied without any memory allocations.

Obtaining the capacity of the collection must take a constant amount of time and space.

Required Methods

fn capacity(&self) -> usize

Returns the capacity of the collection.

If this collection stores zero-sized types, then it effectively has infinite capacity. For this reason, those collections should have a capacity of usize::MAX.

Examples

use len_trait::Capacity;

fn check_capacity<C: Capacity>(collection: C, zero_sized: bool) {
    if zero_sized {
        assert_eq!(collection.capacity(), usize::max_value());
    } else {
        assert!(collection.capacity() >= collection.len());
    }
}

check_capacity(vec![()], true);
check_capacity(vec![1, 2, 3], false);
check_capacity("Hello, world!".to_string(), false);

Implementations on Foreign Types

impl Capacity for String

fn capacity(&self) -> usize

impl Capacity for OsString

fn capacity(&self) -> usize

impl<K: Eq + Hash, V> Capacity for HashMap<K, V>

fn capacity(&self) -> usize

impl<T> Capacity for VecDeque<T>

fn capacity(&self) -> usize

impl<T> Capacity for Vec<T>

fn capacity(&self) -> usize

impl<T: Eq + Hash> Capacity for HashSet<T>

fn capacity(&self) -> usize

impl<T: Ord> Capacity for BinaryHeap<T>

fn capacity(&self) -> usize

impl<T: ?Sized + Capacity> Capacity for Box<T>

fn capacity(&self) -> usize

impl<T: ?Sized + Capacity> Capacity for Rc<T>

fn capacity(&self) -> usize

impl<T: ?Sized + Capacity> Capacity for Arc<T>

fn capacity(&self) -> usize

Implementors