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// SPDX-License-Identifier: CC0-1.0
//! Provides a wrapper for types that can technically implement `PartialOrd`/`Ord`
//! but for semantic reasons it is nonsensical.
//!
//! For examples see the docs on [`Ordered`] or the code in `examples/point.rs`.
#![no_std]
// Experimental features we need.
#![cfg_attr(docsrs, feature(doc_auto_cfg))]
// Coding conventions.
#![warn(missing_docs)]
use core::borrow::{Borrow, BorrowMut};
use core::cmp::Ordering;
use core::fmt;
use core::ops::{Deref, DerefMut};
/// Trait for types that perform an arbitrary ordering.
///
/// More specifically, this trait is for types that perform either a partial or
/// total order but semantically it is nonsensical.
pub trait ArbitraryOrd: Eq + PartialEq {
/// Implements a meaningless, arbitrary ordering.
fn arbitrary_cmp(&self, other: &Self) -> Ordering;
}
/// A wrapper type that implements `PartialOrd` and `Ord`.
///
/// # Examples
///
/// ```
/// use core::{cmp::Ordering, fmt};
/// use ordered::{ArbitraryOrd, Ordered};
///
/// /// 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 {
/// // Just use whatever order tuple cmp gives us.
/// (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)
/// }
/// }
///
/// let point = Point { x: 0, y: 1 };
/// let ordered = Ordered(point);
///
/// println!("We can explicitly deref (*ordered): {}", *ordered);
/// println!("Or use deref coercion (ordered): {}", ordered);
/// println!("Or we can use borrow (&ordered): {}", &ordered);
/// ```
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
#[repr(transparent)]
pub struct Ordered<T>(pub T);
impl<T: Copy> Copy for Ordered<T> {}
impl<T> Ordered<T> {
/// Creates a new wrapped ordered type.
///
/// The inner type is public so this function is never explicitly needed.
pub const fn new(inner: T) -> Self { Self(inner) }
/// Returns a reference to the inner object.
///
/// We also implement [`core::borrow::Borrow`] so this function is never explicitly needed.
pub const fn as_inner(&self) -> &T { &self.0 }
/// Returns the inner object.
///
/// We also implement [`core::ops::Deref`] so this function is never explicitly needed.
pub fn into_inner(self) -> T { self.0 }
/// Creates an `Ordered<T>` from a reference.
///
/// This allows: `let found = map.get(Ordered::from_ref(&a));`
pub fn from_ref(value: &T) -> &Self {
unsafe { &*(value as *const _ as *const Self) }
}
}
impl<T: ArbitraryOrd> ArbitraryOrd for &T {
fn arbitrary_cmp(&self, other: &Self) -> Ordering {
(*self).arbitrary_cmp(other)
}
}
impl<T: ArbitraryOrd> PartialOrd for Ordered<T> {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> { Some(self.cmp(other)) }
}
impl<T: ArbitraryOrd> Ord for Ordered<T> {
fn cmp(&self, other: &Self) -> Ordering { self.0.arbitrary_cmp(&other.0) }
}
impl<T: fmt::Display> fmt::Display for Ordered<T> {
fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result { fmt::Display::fmt(&self.0, f) }
}
impl<T> From<T> for Ordered<T> {
fn from(inner: T) -> Self { Self(inner) }
}
impl<T> AsRef<T> for Ordered<T> {
fn as_ref(&self) -> &T { &self.0 }
}
impl<T> AsMut<T> for Ordered<T> {
fn as_mut(&mut self) -> &mut T { &mut self.0 }
}
impl<T> Borrow<T> for Ordered<T> {
fn borrow(&self) -> &T { &self.0 }
}
impl<T> BorrowMut<T> for Ordered<T> {
fn borrow_mut(&mut self) -> &mut T { &mut self.0 }
}
impl<T> Deref for Ordered<T> {
type Target = T;
fn deref(&self) -> &Self::Target { &self.0 }
}
impl<T> DerefMut for Ordered<T> {
fn deref_mut(&mut self) -> &mut T { &mut self.0 }
}
#[cfg(test)]
mod tests {
use super::*;
#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
struct Point {
x: u32,
y: u32,
}
impl Point {
fn new(x: u32, y: u32) -> Self { Point { x, y } }
}
impl ArbitraryOrd for Point {
fn arbitrary_cmp(&self, other: &Self) -> Ordering { (self.x, self.y).cmp(&(other.x, other.y)) }
}
#[test]
fn can_compare() {
let a = Point::new(2, 3);
let b = Point::new(5, 7);
assert!(Ordered(a) < Ordered(b));
}
#[test]
fn can_compare_with_from_ref() {
let a = Point::new(2, 3);
let b = Point::new(5, 7);
assert!(Ordered::from_ref(&a) < Ordered::from_ref(&b));
}
#[test]
fn can_compare_with_reference() {
let a = Point::new(2, 3);
let b = Point::new(5, 7);
assert!(Ordered(&a) < Ordered(&b));
}
}