Module alloc::boxed
[−]
[src]
A pointer type for heap allocation.
Box<T>
, casually referred to as a 'box', provides the simplest form of
heap allocation in Rust. Boxes provide ownership for this allocation, and
drop their contents when they go out of scope.
Examples
Creating a box:
let x = Box::new(5);
Creating a recursive data structure:
#[derive(Debug)] enum List<T> { Cons(T, Box<List<T>>), Nil, } fn main() { let list: List<i32> = List::Cons(1, Box::new(List::Cons(2, Box::new(List::Nil)))); println!("{:?}", list); }
This will print Cons(1, Cons(2, Nil))
.
Recursive structures must be boxed, because if the definition of Cons
looked like this:
Cons(T, List<T>),
It wouldn't work. This is because the size of a List
depends on how many
elements are in the list, and so we don't know how much memory to allocate
for a Cons
. By introducing a Box
, which has a defined size, we know how
big Cons
needs to be.
Structs
Box 
A pointer type for heap allocation. 
ExchangeHeapSingleton 
[Unstable] This the singleton type used solely for 
IntermediateBox 
[Unstable]

Constants
HEAP 
[Unstable] A value that represents the heap. This is the default place that the 
Traits
FnBox 
[Unstable]
