On Dec 25, 2013, at 5:17 PM, Vadim <[email protected]> wrote:
> I agree that unexpected mutation is undesirable, but:
> - requiring 'mut' is orthogonal to requiring '&' sigil, IMHO,
> - as currently implemented, Rust does not always require mut when callee
> mutates the argument, for example:
>
> fn main() {
> let mut i: int = 0;
> foo(&mut i);
> println!("{}", i);
> }
> fn foo(i: &mut int) {
> bar(i); // no mut!
> }
> fn bar(i: &mut int) {
> *i = *i + 1;
> }
>
> Note that invocation of bar() inside foo() does not forewarn reader by
> requiring 'mut'. Wouldn't you rather see this?:
>
> fn main() {
> let mut i: int = 0;
> foo(mut i);
> println!("{}", i);
> }
> fn foo(i: &mut int) {
> bar(mut i);
> }
> fn bar(i: &mut int) {
> i = i + 1;
> }
What is the point of adding `mut` here? bar() does not need `mut` because
calling bar(i) does not auto-borrow i. It’s already a `&mut int`.
-Kevin
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