Mut

If a value is mutable it must be declared with mut.

But beware, the pointer madness it not all gone.

Lets say you want to find a customer in a list and be able to mutate this customer:

fn (mut tm Timemanager) find_customer(id string) ?&Customer {
    for mut c in tm.customers {
        if c.id == id {
            return c
        }
    }
    return none
}

Even though c is declared as mut , you must return a pointer from the function to be able to mutate c outside this function. And there is no warning if you do not.

Its not possible to use mut in the return type declaration.