任意排序

为可以技术上实现 PartialOrd/Ord 的类型提供包装器，但出于语义原因，为该类型实现全序是没有意义的。

示例

您可能想将一个类型用作 BTreeMap 中的键，这需要 Ord，尽管为该类型实现全序可能没有意义。

use std::cmp::Ordering;
use std::collections::BTreeMap;
use ordered::{ArbitraryOrd, Ordered};

/// A Foo type.
///
/// We do not want users to be able to write `a < b` because it is meaningless
/// to compare the two but we wish to use `Foo`, for example, as a `BTreeMap` key.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
enum Foo {
    /// A space foo.
    Space(u32),
    /// A time foo.
    Time(u32)
}

impl ArbitraryOrd for Foo {
    fn arbitrary_cmp(&self, other: &Self) -> Ordering {
        use Foo::*;
        match (self, other) {
            (Space(_), Time(_)) => Ordering::Less,
            (Time(_), Space(_)) => Ordering::Greater,
            (Space(this), Space(that)) => this.cmp(that),
            (Time(this), Time(that)) => this.cmp(that),
        }
    }
}

let a = Foo::Space(50);
let b = Foo::Time(50);

let mut map = BTreeMap::new();

// error[E0277]: the trait bound `Foo: Ord` is not satisfied
// map.insert(a, "some interesting value");

map.insert(Ordered(a), "some interesting value");
map.insert(Ordered(b), "some other interesting value");

也许您想在一个包含不实现 Ord 的类型的复杂类型上派生 Ord。

/// An example struct that contains a `Foo` but derives `PartialOrd` and `Ord`.
#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash)]
struct Adt {
    x: u32,
    p: Ordered<Foo>,
}

// Then there are various ways to get at the inner data.

let adt = Adt { x: 42, p: Foo::Space(50).into() };

println!("We can explicitly deref: {}", *adt.p);
println!("Or use deref coercion: {}", adt.p);
println!("Or we can use borrow: {}", &adt.p);

// And if all that is too complicated just use the inherent methods:

println!("Explicitly get a reference: {}", adt.p.as_inner());
println!("Or the inner type: {}", adt.p.into_inner());

最低支持的Rust版本 (MSRV)

该包的MSRV是Rust v1.56.1

许可

本项目的代码根据 Creative Commons CC0 1.0 Universal license 许可。我们使用 SPDX 许可列表 和 SPDX IDs。