rust/src/test/compile-fail/unboxed-closure-feature-gate.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.

// Check that parenthetical notation is feature-gated except with the
// `Fn` traits.

use std::marker;

trait Foo<A> {
    type Output;

    fn dummy(&self, a: A) { }
}

fn main() {
    let x: Box<Foo(isize)>;
    //~^ ERROR parenthetical notation is only stable when used with `Fn`-family

    // No errors with these:
    let x: Box<Fn(isize)>;
    let x: Box<FnMut(isize)>;
    let x: Box<FnOnce(isize)>;
}