Struct SmallBox

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pub struct SmallBox<T: ?Sized, Space> { /* private fields */ }

Expand description

An optimized box that store value on stack or on heap depending on its size

Implementations§

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impl<T: ?Sized, Space> SmallBox<T, Space>

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pub fn new(val: T) -> SmallBox<T, Space> ⓘ
where T: Sized,

Box value on stack or on heap depending on its size.

§Example

use smallbox::SmallBox;
use smallbox::space::*;

let small: SmallBox<_, S4> = SmallBox::new([0usize; 2]);
let large: SmallBox<_, S4> = SmallBox::new([1usize; 8]);

assert_eq!(small.len(), 2);
assert_eq!(large[7], 1);

assert!(large.is_heap() == true);

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pub fn resize<ToSpace>(self) -> SmallBox<T, ToSpace> ⓘ

Change the capacity of SmallBox.

This method may move stack-allocated data from stack to heap when inline space is not sufficient. Once the data is moved to heap, it will never be moved back to stack.

§Example

use smallbox::SmallBox;
use smallbox::space::S2;
use smallbox::space::S4;

let s: SmallBox<_, S4> = SmallBox::new([0usize; 4]);
let m: SmallBox<_, S2> = s.resize();

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pub fn is_heap(&self) -> bool

Returns true if data is allocated on heap.

§Example

use smallbox::SmallBox;
use smallbox::space::S1;

let stacked: SmallBox<usize, S1> = SmallBox::new(0usize);
assert!(!stacked.is_heap());

let heaped: SmallBox<(usize, usize), S1> = SmallBox::new((0usize, 1usize));
assert!(heaped.is_heap());

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pub fn into_inner(self) -> T
where T: Sized,

Consumes the SmallBox and returns ownership of the boxed value

§Examples

use smallbox::SmallBox;
use smallbox::space::S1;

let stacked: SmallBox<_, S1> = SmallBox::new([21usize]);
let val = stacked.into_inner();
assert_eq!(val[0], 21);

let boxed: SmallBox<_, S1> = SmallBox::new(vec![21, 56, 420]);
let val = boxed.into_inner();
assert_eq!(val[1], 56);

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pub fn from_box(boxed: Box<T>) -> Self

Creates a SmallBox from a standard Box.

The data will always be stored on the heap since it’s already allocated there. This method transfers ownership from the Box to the SmallBox without copying or moving the data.

§Example


use smallbox::SmallBox;
use smallbox::space::S4;

let boxed = Box::new([1, 2, 3, 4]);
let small_box: SmallBox<_, S4> = SmallBox::from_box(boxed);

assert!(small_box.is_heap());
assert_eq!(*small_box, [1, 2, 3, 4]);

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pub fn into_box(boxed: SmallBox<T, Space>) -> Box<T>

Converts a SmallBox into a standard Box.

If the data is stored on the stack, it will be moved to the heap. If the data is already on the heap, ownership is transferred without copying or moving the data.

§Example


use smallbox::SmallBox;
use smallbox::space::S4;

let small_box: SmallBox<_, S4> = SmallBox::new([1, 2, 3, 4]);
let boxed: Box<[i32; 4]> = SmallBox::into_box(small_box);

assert_eq!(*boxed, [1, 2, 3, 4]);

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impl<Space> SmallBox<dyn Any, Space>

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pub fn downcast<T: Any>(self) -> Result<SmallBox<T, Space>, Self>

Attempt to downcast the box to a concrete type.

§Examples

#[macro_use]
extern crate smallbox;

use core::any::Any;

use smallbox::SmallBox;
use smallbox::space::*;

fn print_if_string(value: SmallBox<dyn Any, S1>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

fn main() {
    let my_string = "Hello World".to_string();
    print_if_string(smallbox!(my_string));
    print_if_string(smallbox!(0i8));
}

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impl<Space> SmallBox<dyn Any + Send, Space>

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pub fn downcast<T: Any>(self) -> Result<SmallBox<T, Space>, Self>

Attempt to downcast the box to a concrete type.

§Examples

#[macro_use]
extern crate smallbox;

use core::any::Any;

use smallbox::SmallBox;
use smallbox::space::*;

fn print_if_string(value: SmallBox<dyn Any, S1>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

fn main() {
    let my_string = "Hello World".to_string();
    print_if_string(smallbox!(my_string));
    print_if_string(smallbox!(0i8));
}