src/test/run-pass/deriving-cmp-shortcircuit.rs

// Copyright 2013 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 the derived impls for the comparison traits shortcircuit
// where possible, by having a type that fails when compared as the
// second element, so this passes iff the instances shortcircuit.

pub struct FailCmp;
impl PartialEq for FailCmp {
    fn eq(&self, _: &FailCmp) -> bool { fail!("eq") }
}

impl PartialOrd for FailCmp {
    fn lt(&self, _: &FailCmp) -> bool { fail!("lt") }
}

impl Eq for FailCmp {}

impl Ord for FailCmp {
    fn cmp(&self, _: &FailCmp) -> Ordering { fail!("cmp") }
}

#[deriving(PartialEq,PartialOrd,Eq,Ord)]
struct ShortCircuit {
    x: int,
    y: FailCmp
}

pub fn main() {
    let a = ShortCircuit { x: 1, y: FailCmp };
    let b = ShortCircuit { x: 2, y: FailCmp };

    assert!(a != b);
    assert!(a < b);
    assert_eq!(a.cmp(&b), ::std::cmp::Less);
}