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;
}
On Tue, Dec 24, 2013 at 6:10 PM, comex <[email protected]> wrote:
> On Tue, Dec 24, 2013 at 8:17 PM, Vadim <[email protected]> wrote:
> > I'm again pretty nervous about this, because this is one of the
> > much-maligned features of C++ references.
> >
> >
> > Why is it maligned, though?
>
> I malign it mainly because it allows (and encourages) confusing code
> that looks like it's calling a function with a variable as an argument
> but actually mutates the variable. Arguably, only auto-borrowing
> immutably would sidestep this issue.
>
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