Mutability (mut)

Silk is safe-by-default: bindings and borrows are immutable unless you opt in to mutation.

Full reference: mutability.

Notes#

• Supported forms + borrow rules: mutability

Syntax#

let mut x: int = 0;
x += 1;

// Two-part mut borrow contract:
// - parameter declared `mut`, and
// - call site uses `mut <expr>`.
// fn bump(mut p: &Pair) -> void { ... }
// bump(mut pair);

Example: mutable local + mutable borrow#

struct Pair {
  a: int,
  b: int,
}

fn bump_a (mut p: &Pair) -> void {
  p.a += 1;
}

fn main () -> int {
  let mut p: Pair = Pair{ a: 1, b: 2 };
  bump_a(mut p);
  return p.a;
}

See also#

• Full reference: mutability
• Borrow-checker design notes: borrow checker