# Values never change

Every value is immutable. Passing a value to a function or returning it never
lets anyone else change it. A local declared with `var mut` can be pointed at a
new value of the same type, but fields cannot be assigned: to change an object,
build a new one.

```jadpo
type Product = Object {
    name: ProductName
    stock: Stock
}

function restock(product: Product, stock: Stock) -> Product {
    return Product {
        name: product.name
        stock: stock
    }
}
```