rust/src/test/run-pass/issue-17897.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.

#![feature(unboxed_closures, std_misc)]

use std::thunk::Thunk;

fn action(cb: Thunk<(usize,), usize>) -> usize {
    cb(1)
}

pub fn main() {
    println!("num: {}", action(Box::new(move |u| u)));
}