7b25e88602
The wording of RFC #495 enables moves out of slices. Unfortuantely, non-zeroing moves out of slices introduce a very annoying complication: as slices can vary in their length, indexes from the start and end may or may not overlap depending on the slice's exact length, which prevents assigning a particular drop flag for each individual element. For example, in the code ```Rust fn foo<T>(a: Box<[Box<[T]>]>, c: bool) -> T { match (a, c) { (box [box [t, ..], ..], true) => t, (box [.., box [.., t]], false) => t, _ => panic!() } } ``` If the condition is false, we have to drop the first element of `a`, unless `a` has size 1 in which case we drop all the elements of it but the last. If someone comes with a nice way of handling it, we can always re-allow moves out of slices. This is a [breaking-change], but it is behind the `slice_patterns` feature gate and was not allowed until recently.
22 lines
671 B
Rust
22 lines
671 B
Rust
// Copyright 2016 The Rust Project Developers. See the COPYRIGHT
|
|
// file at the top-level directory of this distribution and at
|
|
// http://rust-lang.org/COPYRIGHT.
|
|
//
|
|
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
|
|
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
|
|
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
|
|
// option. This file may not be copied, modified, or distributed
|
|
// except according to those terms.
|
|
|
|
#![feature(slice_patterns, box_patterns)]
|
|
|
|
struct A;
|
|
|
|
fn main() {
|
|
let a: Box<[A]> = Box::new([A]);
|
|
match a {
|
|
box [a] => {}, //~ ERROR cannot move out of type `[A]`
|
|
_ => {}
|
|
}
|
|
}
|