Trait script::dom::bindings::import::module::cmp::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)

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 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, 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 script::dom::bindings::import::module::cmp::PartialOrd

Required Methods§

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

Implementors§

impl PartialOrd<BigEndian> for BigEndian

impl PartialOrd<LittleEndian> for LittleEndian

impl PartialOrd<WebGLVersion> for WebGLVersion

impl PartialOrd<Month> for Month

impl PartialOrd<LabelStyle> for LabelStyle

impl PartialOrd<Severity> for Severity

impl PartialOrd<Meaning> for Meaning

impl PartialOrd<SectionId> for SectionId

impl PartialOrd<ColumnType> for ColumnType

impl PartialOrd<AttrValueKind> for AttrValueKind

impl PartialOrd<DoctypeIdKind> for DoctypeIdKind

impl PartialOrd<RawKind> for RawKind

impl PartialOrd<ScriptEscapeKind> for ScriptEscapeKind

impl PartialOrd<State> for html5ever::tokenizer::states::State

impl PartialOrd<ExtensionType> for ExtensionType

impl PartialOrd<LocaleFallbackPriority> for LocaleFallbackPriority

impl PartialOrd<LocaleFallbackSupplement> for LocaleFallbackSupplement

impl PartialOrd<NormalForm> for NormalForm

impl PartialOrd<Level> for log::Level

impl PartialOrd<Level> for log::LevelFilter

impl PartialOrd<LevelFilter> for log::Level

impl PartialOrd<LevelFilter> for log::LevelFilter

impl PartialOrd<AddressSpace> for AddressSpace

impl PartialOrd<ArraySize> for ArraySize

impl PartialOrd<AtomicFunction> for AtomicFunction

impl PartialOrd<BinaryOperator> for BinaryOperator

impl PartialOrd<BuiltIn> for naga::BuiltIn

impl PartialOrd<ConservativeDepth> for ConservativeDepth

impl PartialOrd<DerivativeAxis> for DerivativeAxis

impl PartialOrd<DerivativeControl> for DerivativeControl

impl PartialOrd<ImageClass> for ImageClass

impl PartialOrd<ImageDimension> for ImageDimension

impl PartialOrd<Interpolation> for Interpolation

impl PartialOrd<Literal> for naga::Literal

impl PartialOrd<MathFunction> for MathFunction

impl PartialOrd<RelationalFunction> for RelationalFunction

impl PartialOrd<Sampling> for Sampling

impl PartialOrd<ScalarKind> for ScalarKind

impl PartialOrd<ShaderStage> for ShaderStage

impl PartialOrd<StorageFormat> for StorageFormat

impl PartialOrd<SwizzleComponent> for SwizzleComponent

impl PartialOrd<UnaryOperator> for UnaryOperator

impl PartialOrd<VectorSize> for VectorSize

impl PartialOrd<Direction> for petgraph::Direction

impl PartialOrd<ProfilerCategory> for ProfilerCategory

impl PartialOrd<TimerMetadataFrameType> for TimerMetadataFrameType

impl PartialOrd<TimerMetadataReflowType> for TimerMetadataReflowType

impl PartialOrd<Channels> for Channels

impl PartialOrd<ColorSpace> for ColorSpace

impl PartialOrd<Utf8Sequence> for Utf8Sequence

impl PartialOrd<Number> for ron::value::Number

impl PartialOrd<Value> for ron::value::Value

impl PartialOrd<Direction> for rustix::ioctl::Direction

impl PartialOrd<SocketAddrAny> for SocketAddrAny

impl PartialOrd<Void> for servo_media_audio::graph::Void

impl PartialOrd<ParamDir> for ParamDir

impl PartialOrd<ParamType> for ParamType

impl PartialOrd<AccessQualifier> for AccessQualifier

impl PartialOrd<AddressingModel> for AddressingModel

impl PartialOrd<BuiltIn> for spirv::BuiltIn

impl PartialOrd<CLOp> for CLOp

impl PartialOrd<Capability> for Capability

impl PartialOrd<Decoration> for Decoration

impl PartialOrd<Dim> for Dim

impl PartialOrd<ExecutionMode> for ExecutionMode

impl PartialOrd<ExecutionModel> for ExecutionModel

impl PartialOrd<FPRoundingMode> for FPRoundingMode

impl PartialOrd<FunctionParameterAttribute> for FunctionParameterAttribute

impl PartialOrd<GLOp> for GLOp

impl PartialOrd<GroupOperation> for GroupOperation

impl PartialOrd<ImageChannelDataType> for ImageChannelDataType