Trait scrypto::prelude::PartialOrd

1.0.0 · source ·

pub trait PartialOrd<Rhs = Self>: PartialEq<Rhs>where
    Rhs: ?Sized,{
    // Required method
    fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>;

    // Provided methods
    fn lt(&self, other: &Rhs) -> bool { ... }
    fn le(&self, other: &Rhs) -> bool { ... }
    fn gt(&self, other: &Rhs) -> bool { ... }
    fn ge(&self, other: &Rhs) -> bool { ... }
}

Expand description

Trait for types that form a partial order.

The lt, le, gt, and ge methods of this trait can be called using the <, <=, >, and >= operators, respectively.

The methods of this trait must be consistent with each other and with those of PartialEq. The following conditions must hold:

a == b if and only if partial_cmp(a, b) == Some(Equal).
a < b if and only if partial_cmp(a, b) == Some(Less)
a > b if and only if partial_cmp(a, b) == Some(Greater)
a <= b if and only if a < b || a == b
a >= b if and only if a > b || a == b
a != b if and only if !(a == b).

Conditions 2–5 above are ensured by the default implementation. Condition 6 is already ensured by PartialEq.

If Ord is also implemented for Self and Rhs, it must also be consistent with partial_cmp (see the documentation of that trait for the exact requirements). It’s easy to accidentally make them disagree by deriving some of the traits and manually implementing others.

The comparison must satisfy, for all a, b and c:

transitivity: a < b and b < c implies a < c. The same must hold for both == and >.
duality: a < b if and only if b > a.

Note that these requirements mean that the trait itself must be implemented symmetrically and transitively: if T: PartialOrd and U: PartialOrd<V> then U: PartialOrd<T> and T: PartialOrd<V>.

Violating these requirements is a logic error. The behavior resulting from a logic error is not specified, but users of the trait must ensure that such logic errors do not result in undefined behavior. This means that unsafe code must not rely on the correctness of these methods.

§Corollaries

The following corollaries follow from the above requirements:

irreflexivity of < and >: !(a < a), !(a > a)
transitivity of >: if a > b and b > c then a > c
duality of partial_cmp: partial_cmp(a, b) == partial_cmp(b, a).map(Ordering::reverse)

§Strict and non-strict partial orders

The < and > operators behave according to a strict partial order. However, <= and >= do not behave according to a non-strict partial order. That is because mathematically, a non-strict partial order would require reflexivity, i.e. a <= a would need to be true for every a. This isn’t always the case for types that implement PartialOrd, for example:

let a = f64::sqrt(-1.0);
assert_eq!(a <= a, false);

§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 primarily ordered by their discriminants. Secondarily, they are ordered by their fields. By default, the discriminant is smallest for variants at the top, and largest for variants at the bottom. Here’s an example:

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

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

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

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

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

§How can I implement `PartialOrd`?

PartialOrd only requires implementation of the partial_cmp method, with the others generated from default implementations.

However it remains possible to implement the others separately for types which do not have a total order. For example, for floating point numbers, NaN < 0 == false and NaN >= 0 == false (cf. IEEE 754-2008 section 5.11).

PartialOrd requires your type to be PartialEq.

If your type is Ord, you can implement partial_cmp by using cmp:

use std::cmp::Ordering;

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

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

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

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

You may also find it useful to use partial_cmp on your type’s fields. Here is an example of Person types who have a floating-point height field that is the only field to be used for sorting:

use std::cmp::Ordering;

struct Person {
    id: u32,
    name: String,
    height: f64,
}

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

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

§Examples

let x: u32 = 0;
let y: u32 = 1;

assert_eq!(x < y, true);
assert_eq!(x.lt(&y), true);

Required Methods§

source

fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

§Examples

use std::cmp::Ordering;

let result = 1.0.partial_cmp(&2.0);
assert_eq!(result, Some(Ordering::Less));

let result = 1.0.partial_cmp(&1.0);
assert_eq!(result, Some(Ordering::Equal));

let result = 2.0.partial_cmp(&1.0);
assert_eq!(result, Some(Ordering::Greater));

When comparison is impossible:

let result = f64::NAN.partial_cmp(&1.0);
assert_eq!(result, None);

Provided Methods§

source

fn lt(&self, other: &Rhs) -> bool

This method tests less than (for self and other) and is used by the < operator.

§Examples

assert_eq!(1.0 < 1.0, false);
assert_eq!(1.0 < 2.0, true);
assert_eq!(2.0 < 1.0, false);

source

fn le(&self, other: &Rhs) -> bool

This method tests less than or equal to (for self and other) and is used by the <= operator.

§Examples

assert_eq!(1.0 <= 1.0, true);
assert_eq!(1.0 <= 2.0, true);
assert_eq!(2.0 <= 1.0, false);

source

fn gt(&self, other: &Rhs) -> bool

This method tests greater than (for self and other) and is used by the > operator.

§Examples

assert_eq!(1.0 > 1.0, false);
assert_eq!(1.0 > 2.0, false);
assert_eq!(2.0 > 1.0, true);

source

fn ge(&self, other: &Rhs) -> bool

This method tests greater than or equal to (for self and other) and is used by the >= operator.

§Examples

assert_eq!(1.0 >= 1.0, true);
assert_eq!(1.0 >= 2.0, false);
assert_eq!(2.0 >= 1.0, true);

Trait scrypto::prelude::PartialOrd

§Corollaries

§Strict and non-strict partial orders

§Derivable

§How can I implement PartialOrd?

§Examples

Required Methods§

fn partial_cmp(&self, other: &Rhs) -> Option<Ordering>

§Examples

Provided Methods§

fn lt(&self, other: &Rhs) -> bool

§Examples

fn le(&self, other: &Rhs) -> bool

§Examples

fn gt(&self, other: &Rhs) -> bool

§Examples

fn ge(&self, other: &Rhs) -> bool

§Examples

Implementors§

impl PartialOrd for AttachedModuleId

impl PartialOrd for ModuleId

impl PartialOrd for Proposer

impl PartialOrd for Role

impl PartialOrd for DefaultDepositRule

impl PartialOrd for ResourcePreference

impl PartialOrd for PartitionDescription

impl PartialOrd for AccessRule

impl PartialOrd for AccessRuleNode

impl PartialOrd for MethodAccessibility

impl PartialOrd for OwnerRoleUpdater

impl PartialOrd for ProofRule

impl PartialOrd for ResourceFeature

impl PartialOrd for ResourceOrNonFungible

impl PartialOrd for ManifestAddress

impl PartialOrd for NonFungibleIdType

impl PartialOrd for NonFungibleLocalId

impl PartialOrd for BlueprintHook

impl PartialOrd for AccessControllerPartitionOffset

impl PartialOrd for AccountPartitionOffset

impl PartialOrd for AuthZoneField

impl PartialOrd for BootLoaderField

impl PartialOrd for ComponentField

impl PartialOrd for ComponentRoyaltyPartitionOffset

impl PartialOrd for ConsensusManagerPartitionOffset

impl PartialOrd for EntityType

impl PartialOrd for FungibleBucketField

impl PartialOrd for FungibleProofField

impl PartialOrd for FungibleResourceManagerPartitionOffset

impl PartialOrd for FungibleVaultPartitionOffset

impl PartialOrd for Level

impl PartialOrd for MetadataPartitionOffset

impl PartialOrd for MultiResourcePoolPartitionOffset

impl PartialOrd for NonFungibleBucketField

impl PartialOrd for NonFungibleProofField

impl PartialOrd for NonFungibleResourceManagerPartitionOffset

impl PartialOrd for NonFungibleVaultPartitionOffset

impl PartialOrd for OneResourcePoolPartitionOffset

impl PartialOrd for PackagePartitionOffset

impl PartialOrd for RoleAssignmentPartitionOffset

impl PartialOrd for RoyaltyField

impl PartialOrd for SubstateKey

impl PartialOrd for TransactionTrackerField

impl PartialOrd for TwoResourcePoolPartitionOffset

impl PartialOrd for TypeInfoField

impl PartialOrd for ValidatorPartitionOffset

impl PartialOrd for WorktopField

impl PartialOrd for AsciiChar

impl PartialOrd for IpAddr

impl PartialOrd for SocketAddr

impl PartialOrd for ErrorKind

impl PartialOrd for Sign

impl PartialOrd for Ordering

impl PartialOrd for Infallible

impl PartialOrd for bool

impl PartialOrd for char

impl PartialOrd for f32

impl PartialOrd for f64

impl PartialOrd for i8

impl PartialOrd for i16

impl PartialOrd for i32

§How can I implement `PartialOrd`?