Impl ArbitraryOrd for std smart pointers and various generic types

[Kixunil]

• Box
• Rc
• Arc
• [T]
• Vec
• Option
• Result
• ManuallyDrop

Basically anything that has Ord already.

[tcharding]

What is the use case? I tried to think it through for Vec but I got to this code that builds already.

/// A point in 2D space.
///
/// We do not want users to be able to write `a < b` because it is not well defined.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
struct Point {
    x: u32,
    y: u32,
}

impl ArbitraryOrd for Point {
    fn arbitrary_cmp(&self, other: &Self) -> Ordering { (self.x, self.y).cmp(&(other.x, other.y)) }
}

impl fmt::Display for Point {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { write!(f, "({}, {})", self.x, self.y) }
}

/// A type that derives `Ord` and friends.
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct Adt {
    // point: Point,  // Doesn't build, this is the reason we provide `Ordered`.
    point: Ordered<Point>,
    // v: Vec<Point>, // Also doesn't build but we can wrap in `Ordered` again.
    v: Vec<Ordered<Point>>,
}

[Kixunil]

The use case is being able to write things like BTreeMap<Ordered<Box<HugeStructWithArbitrarryOrd>>> etc. Generally, crates implement their traits for all sensible std types. For Vec, dealing with Ordered<Vec<Point>> is very likely less annoying than Vec<Ordered<Point>.

[tcharding]

I'm cutting the 1.0-alpha release but flagging that I intend on doing this before 1.0