rust/src/test/run-pass/dst-deref.rs

// Copyright 2014 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.

// Test that a custom deref with a fat pointer return type does not ICE


use std::ops::Deref;

pub struct Arr {
    ptr: Box<[usize]>
}

impl Deref for Arr {
    type Target = [usize];

    fn deref(&self) -> &[usize] {
        &*self.ptr
    }
}

pub fn foo(arr: &Arr) {
    assert_eq!(arr.len(), 3);
    let x: &[usize] = &**arr;
    assert_eq!(x[0], 1);
    assert_eq!(x[1], 2);
    assert_eq!(x[2], 3);
}

fn main() {
    // FIXME (#22405): Replace `Box::new` with `box` here when/if possible.
    let a = Arr { ptr: Box::new([1, 2, 3]) };
    foo(&a);
}