Stack and Heap

Table of Contents

Rust defaults to allocation on the stack

Stack Allocation

struct Point {
    x: i32,
    y: i32
}

fn main() {
    let point = Point { x: 1, y: 1};
}

Box

Heap allocation is represented by the type Box.

struct Point {
    x: i32,
    y: i32
}

fn main() {
    let point = Point { x: 1, y: 1};
    let point_on_heap = Box::new(point);
}

Ownership and Borrowing

Box is owned, but you can borrow the contained values.

#[derive(Debug)]
struct Point {
    x: i32,
    y: i32
}

fn main() {
    let point = Point { x: 1, y: 1};
    let point_on_heap = Box::new(point);
    print_point(&point_on_heap);
}

fn print_point(p: &Point) {
    println!("{:?}", p);
}

Other heap allocations

Other types also allocate on the heap, most notably Vec and String.

Placement in

It is currently not possible to allocate values at a self-chosen location. The missing feature is called "placement in".

Detailed discussion here

In most cases, LLVM already optimizes the stack allocation and the subsequent move to the heap to a direct heap allocation.