gistfile1.rs

// Putting #[no_implicit_prelude] on this mod, because we want to
// define and use our own `equals`.

#[no_implicit_prelude]
pub mod default_methods_example {

// Explicitly import this stuff.
use std::clone::Clone;
use std::io::println;

trait Eq {
    fn equals(&self, other: &Self) -> bool;

    fn my_neq(&self, other: &Self) -> bool {
        !self.equals(other)
    }
}


#[deriving(Clone)]
enum Color { cyan, magenta, yellow, black }

impl Eq for Color {
    fn equals(&self, other: &Color) -> bool {
        match (*self, *other) {
          (cyan, cyan)       => { true  }
          (magenta, magenta) => { true  }
          (yellow, yellow)   => { true  }
          (black, black)     => { true  }
          _                  => { false }
        }
    }
}

#[deriving(Clone)]
enum ColorTree {
    leaf(Color),
    branch(@ColorTree, @ColorTree)
}

impl Eq for ColorTree {
    fn equals(&self, other: &ColorTree) -> bool {
        match (*self, *other) {
          (leaf(x), leaf(y)) => { x.equals(&y) }
          (branch(l1, r1), branch(l2, r2)) => {
            l1.equals(&*l2) && r1.equals(&*r2)
          }
          _ => { false }
        }
    }
}

// A bounded polymorphism example -- this is where traits are handy.
fn member<T: Eq + Clone>(elem: &T, vec: ~[T]) -> bool {
    let mut i = 0;

    while i <= vec.len() {

        // Make local copies.
        let elem = elem.clone();
        let vec_elem = vec[i].clone();

        if elem.equals(&vec_elem) { return true; }

        i = i + 1;
    }
    
    return false;
}

pub fn test() {
    assert!( cyan.equals(&cyan) );
    assert!( magenta.equals(&magenta) );
    assert!( !cyan.equals(&yellow) );
    assert!( !magenta.equals(&cyan) );

    println("Assertions all succeeded!");
}

}

pub fn main() {
    use default_methods_example;
    default_methods_example::test();
}

The error I'm getting is

$ ~/repos/rust/x86_64-apple-darwin/stage2/bin/rustc rust-traits-example.rs
rust-traits-example.rs:46:22: 46:26 error: $<2>$<2>mismatched types: expected `&@default_methods_example::ColorTree` but found `&default_methods_example::ColorTree` (expected @-ptr but found enum default_methods_example::ColorTree)
$<2>rust-traits-example.rs:46             l1.equals(&*l2) && r1.equals(&*r2)
                                                ^~~~
$<2>rust-traits-example.rs:46:12: 46:30 error: $<2>$<2>failed to find an implementation of trait std::cmp::TotalEq for default_methods_example::ColorTree
$<2>rust-traits-example.rs:46             l1.equals(&*l2) && r1.equals(&*r2)
                                      ^~~~~~~~~~~~~~~~~~

The first error must be a consequence of the second, because if I just change all occurrences of equals to my_equals it compiles and runs fine.