rust/src/liballoc/tests/arc.rs

// Copyright 2018 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.

use std::any::Any;
use std::sync::{Arc, Weak};

#[test]
fn uninhabited() {
    enum Void {}
    let mut a = Weak::<Void>::new();
    a = a.clone();
    assert!(a.upgrade().is_none());

    let mut a: Weak<dyn Any> = a;  // Unsizing
    a = a.clone();
    assert!(a.upgrade().is_none());
}

#[test]
fn slice() {
    let a: Arc<[u32; 3]> = Arc::new([3, 2, 1]);
    let a: Arc<[u32]> = a;  // Unsizing
    let b: Arc<[u32]> = Arc::from(&[3, 2, 1][..]);  // Conversion
    assert_eq!(a, b);

    // Exercise is_dangling() with a DST
    let mut a = Arc::downgrade(&a);
    a = a.clone();
    assert!(a.upgrade().is_some());
}

#[test]
fn trait_object() {
    let a: Arc<u32> = Arc::new(4);
    let a: Arc<dyn Any> = a;  // Unsizing

    // Exercise is_dangling() with a DST
    let mut a = Arc::downgrade(&a);
    a = a.clone();
    assert!(a.upgrade().is_some());

    let mut b = Weak::<u32>::new();
    b = b.clone();
    assert!(b.upgrade().is_none());
    let mut b: Weak<dyn Any> = b;  // Unsizing
    b = b.clone();
    assert!(b.upgrade().is_none());
}