Values, Not References

● Advanced4 minBefore this: Lists, RecordsSpec 6.1

Every value in Kavach is a value: assigning or passing it never makes two names share it.

fn main() {
    let a = [1, 2, 3]
    let b = a
    b.push(4)
    print(a)
    print(b)
}

kavach run values.kav

[1, 2, 3][1, 2, 3, 4]

b = a gives b its own list. Changing b can't change a. The same holds when you pass a value to a function:

fn add_bonus(scores: [Int]) -> [Int] {
    let changed = scores
    changed.push(100)
    changed
}

fn main() {
    const mine = [70, 80]
    const theirs = add_bonus(mine)
    print(mine)
    print(theirs)
}

kavach run values-fn.kav

[70, 80][70, 80, 100]

In Python, Java or JavaScript, b = a makes two names for one list, and a change through one shows up in the other. That "who else changed my list?" bug can't happen here.

Four levels of control

Level	You write	Use it for
1. Automatic	`nothing`	almost all code
2. Shared state	`Shared<T>`	state several parts of a program change
3. Arenas	`arena { … }`	many short-lived values in a hot path
4. Unsafe	`unsafe { … }`	raw memory and C

What Kavach does for you

Copies are safe, and cheap
Assigning a list gives an independent value, so changing one never changes another. It is only really copied if one of them changes.
spec 6.1