Storage duration and mutability

Meaning of each declaration

format	Allowed Location	reassignment	Use
var	Function/block	possible	Common mutable local variables
const	top	Impossible	Global constant declaration
static	top	possible	Static stored declarations that exist for the life of the program

const PAGE_SIZE: i32 = 4096;
static request_count: i64 = 0;

fun main() {
    var limit: i32 = 4;
    var current: i32 = 0;
    var retries: i32 = 0;

    current += 1;
    retries += 1;
    println("{} {} {}", limit, current, retries);
}

Local declaration rules

var value: i32 = 1;
value = 2;

A new value can be assigned to a local variable declared as var. Constants to be used throughout the program are declared at the top level as const.

Local use of const and static

const and static are top-level declarations. The function body and for initialization use the local declaration var.

Lifespan and Pointers

You can get the address of a local variable as &, but the type ptr<T> does not track the actual lifetime of the storage pointed to by the pointer. When passing a local storage address out of a function, the program structure must directly ensure that the address remains valid.

Learning and Example Range

Practice with the full program · Standard library