Trait nom::lib::std::prelude::v1::rust_2015::Ord 1.0.0[−][src]
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 { ... }
}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 == bora > bis true; and <is transitive:a < bandb < cimpliesa < c. The same must hold for both==and>.
Derivable
This trait can be used with #[derive]. When derived on structs, it will produce a
lexicographic ordering based on the top-to-bottom declaration order of the struct’s members.
When derived on enums, variants are ordered by their top-to-bottom discriminant order.
This means variants at the top are less than variants at the bottom.
Here’s an example:
#[derive(PartialEq, PartialOrd)]
enum Size {
Small,
Large,
}
assert!(Size::Small < Size::Large);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));Implementations on Foreign Types
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.
Implements comparison of vectors lexicographically.
Implements comparison of arrays lexicographically.
Implementors
Implements ordering of vectors, lexicographically.