rust/src/test/run-pass/issue-3052.rs

// Copyright 2012 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.

#![allow(unknown_features)]
#![feature(box_syntax)]

type Connection = Box<FnMut(Vec<u8>) + 'static>;

fn f() -> Option<Connection> {
    let mock_connection: Connection = box |_| {};
    Some(mock_connection)
}

pub fn main() {
}