src/test/compile-fail/dst-bad-assign.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.

// Forbid assignment into a dynamically sized type.

struct Fat<T: ?Sized> {
    f1: isize,
    f2: &'static str,
    ptr: T
}

#[derive(PartialEq,Eq)]
struct Bar;

#[derive(PartialEq,Eq)]
struct Bar1 {
    f: isize
}

trait ToBar {
    fn to_bar(&self) -> Bar;
    fn to_val(&self) -> isize;
}

impl ToBar for Bar1 {
    fn to_bar(&self) -> Bar {
        Bar
    }
    fn to_val(&self) -> isize {
        self.f
    }
}

pub fn main() {
    // Assignment.
    let f5: &mut Fat<ToBar> = &mut Fat { f1: 5, f2: "some str", ptr: Bar1 {f :42} };
    // FIXME (#22405): Replace `Box::new` with `box` here when/if possible.
    let z: Box<ToBar> = Box::new(Bar1 {f: 36});
    f5.ptr = Bar1 {f: 36};
    //~^ ERROR mismatched types
    //~| expected type `ToBar`
    //~| found type `Bar1`
    //~| expected trait ToBar, found struct `Bar1`
    //~| ERROR `ToBar: std::marker::Sized` is not satisfied
}