rust/src/test/run-pass/overload-index-operator.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.

// Test overloading of the `[]` operator.  In particular test that it
// takes its argument *by reference*.

use core::ops::Index;

struct AssociationList<K,V> {
    pairs: ~[AssociationPair<K,V>]
}

struct AssociationPair<K,V> {
    key: K,
    value: V
}

impl<K,V> AssociationList<K,V> {
    fn push(&mut self, key: K, value: V) {
        self.pairs.push(AssociationPair {key: key, value: value});
    }
}

impl<K:Eq,V:Copy> Index<K,V> for AssociationList<K,V> {
    fn index(&self, index: &K) -> V {
        for self.pairs.each |pair| {
            if pair.key == *index {
                return copy pair.value;
            }
        }
        fail!(fmt!("No value found for key: %?", index));
    }
}

pub fn main() {
    let foo = ~"foo";
    let bar = ~"bar";

    let mut list = AssociationList {pairs: ~[]};
    list.push(copy foo, 22);
    list.push(copy bar, 44);

    assert!(list[foo] == 22)
    assert!(list[bar] == 44)

    assert!(list[foo] == 22)
    assert!(list[bar] == 44)
}