Trait scale_info::prelude::cmp::Ord

1.0.0 · source · []
``````pub trait Ord: Eq + PartialOrd<Self> {
fn cmp(&self, other: &Self) -> Ordering;

fn max(self, other: Self) -> Self { ... }
fn min(self, other: Self) -> Self { ... }
fn clamp(self, min: Self, max: Self) -> Self    where        Self: PartialOrd<Self>,
{ ... }
}``````
Expand description

Trait for types that form a total order.

Implementations must be consistent with the `PartialOrd` implementation, and ensure `max`, `min`, and `clamp` are consistent with `cmp`:

• `partial_cmp(a, b) == Some(cmp(a, b))`.
• `max(a, b) == max_by(a, b, cmp)` (ensured by the default implementation).
• `min(a, b) == min_by(a, b, cmp)` (ensured by the default implementation).
• For `a.clamp(min, max)`, see the method docs (ensured by the default implementation).

It’s easy to accidentally make `cmp` and `partial_cmp` disagree by deriving some of the traits and manually implementing others.

Corollaries

From the above and the requirements of `PartialOrd`, it follows that `<` defines a strict total order. This means that for all `a`, `b` and `c`:

• exactly one of `a < b`, `a == b` or `a > b` is true; and
• `<` is transitive: `a < b` and `b < c` implies `a < c`. The same must hold for both `==` and `>`.

Derivable

This trait can be used with `#[derive]`.

When `derive`d on structs, it will produce a lexicographic ordering based on the top-to-bottom declaration order of the struct’s members.

When `derive`d on enums, variants are ordered by their discriminants. By default, the discriminant is smallest for variants at the top, and largest for variants at the bottom. Here’s an example:

``````#[derive(PartialEq, Eq, PartialOrd, Ord)]
enum E {
Top,
Bottom,
}

assert!(E::Top < E::Bottom);``````

However, manually setting the discriminants can override this default behavior:

``````#[derive(PartialEq, Eq, PartialOrd, Ord)]
enum E {
Top = 2,
Bottom = 1,
}

assert!(E::Bottom < E::Top);``````

Lexicographical comparison

Lexicographical comparison is an operation with the following properties:

• Two sequences are compared element by element.
• The first mismatching element defines which sequence is lexicographically less or greater than the other.
• If one sequence is a prefix of another, the shorter sequence is lexicographically less than the other.
• If two sequence have equivalent elements and are of the same length, then the sequences are lexicographically equal.
• An empty sequence is lexicographically less than any non-empty sequence.
• Two empty sequences are lexicographically equal.

How can I implement `Ord`?

`Ord` requires that the type also be `PartialOrd` and `Eq` (which requires `PartialEq`).

Then you must define an implementation for `cmp`. You may find it useful to use `cmp` on your type’s fields.

Here’s an example where you want to sort people by height only, disregarding `id` and `name`:

``````use std::cmp::Ordering;

#[derive(Eq)]
struct Person {
id: u32,
name: String,
height: u32,
}

impl Ord for Person {
fn cmp(&self, other: &Self) -> Ordering {
self.height.cmp(&other.height)
}
}

impl PartialOrd for Person {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
}
}

impl PartialEq for Person {
fn eq(&self, other: &Self) -> bool {
self.height == other.height
}
}``````

Required Methods

This method returns an `Ordering` between `self` and `other`.

By convention, `self.cmp(&other)` returns the ordering matching the expression `self <operator> other` if true.

Examples
``````use std::cmp::Ordering;

assert_eq!(5.cmp(&10), Ordering::Less);
assert_eq!(10.cmp(&5), Ordering::Greater);
assert_eq!(5.cmp(&5), Ordering::Equal);``````

Provided Methods

Compares and returns the maximum of two values.

Returns the second argument if the comparison determines them to be equal.

Examples
``````assert_eq!(2, 1.max(2));
assert_eq!(2, 2.max(2));``````

Compares and returns the minimum of two values.

Returns the first argument if the comparison determines them to be equal.

Examples
``````assert_eq!(1, 1.min(2));
assert_eq!(2, 2.min(2));``````

Restrict a value to a certain interval.

Returns `max` if `self` is greater than `max`, and `min` if `self` is less than `min`. Otherwise this returns `self`.

Panics

Panics if `min > max`.

Examples
``````assert!((-3).clamp(-2, 1) == -2);
assert!(0.clamp(-2, 1) == 0);
assert!(2.clamp(-2, 1) == 1);``````

Implementors

Implements ordering of strings.

Strings are ordered lexicographically by their byte values. This orders Unicode code points based on their positions in the code charts. This is not necessarily the same as “alphabetical” order, which varies by language and locale. Sorting strings according to culturally-accepted standards requires locale-specific data that is outside the scope of the `str` type.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

This trait is implemented for function pointers with up to twelve arguments.

Implements comparison of vectors lexicographically.

This trait is implemented for tuples up to twelve items long.

Implements ordering of vectors, lexicographically.

Implements comparison of arrays lexicographically.