wasmtime_environ::__core::prelude::rust_2024

Trait Ord

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pub trait Ord: Eq + PartialOrd {
    // Required method
    fn cmp(&self, other: &Self) -> Ordering;

    // Provided methods
    fn max(self, other: Self) -> Self
       where Self: Sized { ... }
    fn min(self, other: Self) -> Self
       where Self: Sized { ... }
    fn clamp(self, min: Self, max: Self) -> Self
       where Self: Sized { ... }
}
๐Ÿ”ฌThis is a nightly-only experimental API. (prelude_2024)
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).

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.

ยงCorollaries

From the above and the requirements of PartialOrd, it follows 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 >.

Mathematically speaking, the < operator defines a strict weak order. In cases where == conforms to mathematical equality, it also defines a strict total order.

ยงDerivable

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 structโ€™s members.

When derived on enums, variants are ordered primarily 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. Hereโ€™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);

ยงLexicographical 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 sequences 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.

ยงHow can I implement Ord?

Ord requires that the type also be PartialOrd, PartialEq, and Eq.

Because Ord implies a stronger ordering relationship than PartialOrd, and both Ord and PartialOrd must agree, you must choose how to implement Ord first. You can choose to derive it, or implement it manually. If you derive it, you should derive all four traits. If you implement it manually, you should manually implement all four traits, based on the implementation of Ord.

Hereโ€™s an example where you want to define the Character comparison by health and experience only, disregarding the field mana:

use std::cmp::Ordering;

struct Character {
    health: u32,
    experience: u32,
    mana: f32,
}

impl Ord for Character {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        self.experience
            .cmp(&other.experience)
            .then(self.health.cmp(&other.health))
    }
}

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

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

impl Eq for Character {}

If all you need is to slice::sort a type by a field value, it can be simpler to use slice::sort_by_key.

ยงExamples of incorrect Ord implementations

use std::cmp::Ordering;

#[derive(Debug)]
struct Character {
    health: f32,
}

impl Ord for Character {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        if self.health < other.health {
            Ordering::Less
        } else if self.health > other.health {
            Ordering::Greater
        } else {
            Ordering::Equal
        }
    }
}

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

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

impl Eq for Character {}

let a = Character { health: 4.5 };
let b = Character { health: f32::NAN };

// Mistake: floating-point values do not form a total order and using the built-in comparison
// operands to implement `Ord` irregardless of that reality does not change it. Use
// `f32::total_cmp` if you need a total order for floating-point values.

// Reflexivity requirement of `Ord` is not given.
assert!(a == a);
assert!(b != b);

// Antisymmetry requirement of `Ord` is not given. Only one of a < c and c < a is allowed to be
// true, not both or neither.
assert_eq!((a < b) as u8 + (b < a) as u8, 0);
use std::cmp::Ordering;

#[derive(Debug)]
struct Character {
    health: u32,
    experience: u32,
}

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

impl Ord for Character {
    fn cmp(&self, other: &Self) -> std::cmp::Ordering {
        if self.health < 50 {
            self.health.cmp(&other.health)
        } else {
            self.experience.cmp(&other.experience)
        }
    }
}

// For performance reasons implementing `PartialEq` this way is not the idiomatic way, but it
// ensures consistent behavior between `PartialEq`, `PartialOrd` and `Ord` in this example.
impl PartialEq for Character {
    fn eq(&self, other: &Self) -> bool {
        self.cmp(other) == Ordering::Equal
    }
}

impl Eq for Character {}

let a = Character {
    health: 3,
    experience: 5,
};
let b = Character {
    health: 10,
    experience: 77,
};
let c = Character {
    health: 143,
    experience: 2,
};

// Mistake: The implementation of `Ord` compares different fields depending on the value of
// `self.health`, the resulting order is not total.

// Transitivity requirement of `Ord` is not given. If a is smaller than b and b is smaller than
// c, by transitive property a must also be smaller than c.
assert!(a < b && b < c && c < a);

// Antisymmetry requirement of `Ord` is not given. Only one of a < c and c < a is allowed to be
// true, not both or neither.
assert_eq!((a < c) as u8 + (c < a) as u8, 2);

The documentation of PartialOrd contains further examples, for example itโ€™s wrong for PartialOrd and PartialEq to disagree.

Required Methodsยง

source

fn cmp(&self, other: &Self) -> Ordering

๐Ÿ”ฌThis is a nightly-only experimental API. (prelude_2024)

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.

ยงExamples
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 Methodsยง

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fn max(self, other: Self) -> Self
where Self: Sized,

๐Ÿ”ฌThis is a nightly-only experimental API. (prelude_2024)

Compares and returns the maximum of two values.

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

ยงExamples
assert_eq!(1.max(2), 2);
assert_eq!(2.max(2), 2);
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fn min(self, other: Self) -> Self
where Self: Sized,

๐Ÿ”ฌThis is a nightly-only experimental API. (prelude_2024)

Compares and returns the minimum of two values.

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

ยงExamples
assert_eq!(1.min(2), 1);
assert_eq!(2.min(2), 2);
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fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized,

๐Ÿ”ฌThis is a nightly-only experimental API. (prelude_2024)

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.

ยงPanics

Panics if min > max.

ยงExamples
assert_eq!((-3).clamp(-2, 1), -2);
assert_eq!(0.clamp(-2, 1), 0);
assert_eq!(2.clamp(-2, 1), 1);

Dyn Compatibilityยง

This trait is not dyn compatible.

In older versions of Rust, dyn compatibility was called "object safety", so this trait is not object safe.

Implementorsยง

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impl Ord for EntityIndex

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impl Ord for LibCall

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impl Ord for AsciiChar

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impl Ord for Ordering

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impl Ord for Infallible

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impl Ord for IpAddr

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impl Ord for SocketAddr

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impl Ord for ErrorKind

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impl Ord for Level

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impl Ord for LevelFilter

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impl Ord for bool

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impl Ord for char

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impl Ord for i8

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impl Ord for i16

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impl Ord for i32

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impl Ord for i64

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impl Ord for i128

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impl Ord for isize

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impl Ord for !

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impl Ord for str

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 โ€œalphabeticalโ€ 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.

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impl Ord for u8

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impl Ord for u16

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impl Ord for u32

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impl Ord for u64

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impl Ord for u128

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impl Ord for ()

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impl Ord for usize

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impl Ord for ComponentFuncIndex

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impl Ord for ComponentIndex

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impl Ord for ComponentInstanceIndex

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impl Ord for ComponentTypeIndex

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impl Ord for ComponentUpvarIndex

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impl Ord for DefinedResourceIndex

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impl Ord for ExportIndex

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impl Ord for ImportIndex

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impl Ord for LoweredIndex

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impl Ord for ModuleIndex

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impl Ord for ModuleInstanceIndex

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impl Ord for ModuleUpvarIndex

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impl Ord for ResourceIndex

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impl Ord for RuntimeComponentInstanceIndex

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impl Ord for RuntimeImportIndex

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impl Ord for RuntimeInstanceIndex

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impl Ord for RuntimeMemoryIndex

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impl Ord for RuntimePostReturnIndex

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impl Ord for RuntimeReallocIndex

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impl Ord for StaticComponentIndex

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impl Ord for TrampolineIndex

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impl Ord for TypeComponentIndex

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impl Ord for TypeComponentInstanceIndex

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impl Ord for TypeEnumIndex

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impl Ord for TypeFlagsIndex

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impl Ord for TypeFuncIndex

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impl Ord for TypeListIndex

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impl Ord for TypeModuleIndex

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impl Ord for TypeOptionIndex

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impl Ord for TypeRecordIndex

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impl Ord for TypeResourceTableIndex

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impl Ord for TypeResultIndex

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impl Ord for TypeTupleIndex

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impl Ord for TypeVariantIndex

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impl Ord for String

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impl Ord for BuiltinFunctionIndex

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impl Ord for DataIndex

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impl Ord for DefinedFuncIndex

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impl Ord for DefinedGlobalIndex

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impl Ord for DefinedMemoryIndex

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impl Ord for DefinedTableIndex

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impl Ord for ElemIndex

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impl Ord for EngineInternedRecGroupIndex

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impl Ord for FuncIndex

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impl Ord for FuncRefIndex

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impl Ord for GlobalIndex

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impl Ord for MemoryIndex

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impl Ord for ModuleInternedRecGroupIndex

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impl Ord for ModuleInternedTypeIndex

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impl Ord for OwnedMemoryIndex

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impl Ord for RecGroupRelativeTypeIndex

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impl Ord for StaticModuleIndex

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impl Ord for TableIndex

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impl Ord for TagIndex

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impl Ord for TypeIndex

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impl Ord for VMSharedTypeIndex

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impl Ord for TypeId

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impl Ord for CpuidResult

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impl Ord for CStr

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impl Ord for Error

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impl Ord for PhantomPinned

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impl Ord for Ipv4Addr

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impl Ord for Ipv6Addr

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impl Ord for SocketAddrV4

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impl Ord for SocketAddrV6

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impl Ord for Alignment

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impl Ord for Duration

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impl Ord for CString

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impl Ord for OsStr

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impl Ord for OsString

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impl Ord for Components<'_>

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impl Ord for Path

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impl Ord for PathBuf

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impl Ord for PrefixComponent<'_>

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impl Ord for Instant

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impl Ord for SystemTime

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impl Ord for BuildMetadata

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impl Ord for Prerelease

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impl Ord for Version

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impl Ord for AbstractHeapType

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impl Ord for AliasableResourceId

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impl Ord for AnyTypeId

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impl Ord for ArangeEntry

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impl Ord for ArrayType

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impl Ord for ColumnType

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impl Ord for ComdatId

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impl Ord for ComponentAnyTypeId

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impl Ord for ComponentCoreInstanceTypeId

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impl Ord for ComponentCoreModuleTypeId

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impl Ord for ComponentCoreTypeId

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impl Ord for ComponentDefinedTypeId

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impl Ord for ComponentFuncTypeId

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impl Ord for ComponentInstanceTypeId

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impl Ord for ComponentName

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impl Ord for ComponentNameKind<'_>

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impl Ord for ComponentSectionId

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impl Ord for ComponentTypeId

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impl Ord for ComponentValueTypeId

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impl Ord for CompositeInnerType

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impl Ord for CompositeType

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impl Ord for ContType

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impl Ord for CoreTypeId

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impl Ord for DemangleNodeType

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impl Ord for DwAccess

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impl Ord for DwAddr

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impl Ord for DwAt

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impl Ord for DwAte

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impl Ord for DwCc

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impl Ord for DwCfa

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impl Ord for DwChildren

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impl Ord for DwDefaulted

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impl Ord for DwDs

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impl Ord for DwDsc

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impl Ord for DwEhPe

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impl Ord for DwEnd

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impl Ord for DwForm

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impl Ord for DwId

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impl Ord for DwIdx

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impl Ord for DwInl

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impl Ord for DwLang

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impl Ord for DwLle

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impl Ord for DwLnct

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impl Ord for DwLne

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impl Ord for DwLns

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impl Ord for DwMacro

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impl Ord for DwOp

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impl Ord for DwOrd

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impl Ord for DwRle

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impl Ord for DwSect

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impl Ord for DwSectV2

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impl Ord for DwTag

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impl Ord for DwUt

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impl Ord for DwVirtuality

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impl Ord for DwVis

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impl Ord for FieldType

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impl Ord for FieldType

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impl Ord for FuncType

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impl Ord for HeapType

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impl Ord for KebabStr

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impl Ord for KebabString

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impl Ord for PackedIndex

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impl Ord for Range

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impl Ord for RecGroup

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impl Ord for RecGroupId

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impl Ord for RefType

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impl Ord for RefType

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impl Ord for Register

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impl Ord for ResourceId

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impl Ord for SectionId

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impl Ord for SectionId

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impl Ord for SectionId

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impl Ord for SectionIndex

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impl Ord for StandardSection

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impl Ord for StandardSegment

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impl Ord for StorageType

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impl Ord for StorageType

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impl Ord for StructType

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impl Ord for SubType

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impl Ord for SymbolFlags

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impl Ord for SymbolId

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impl Ord for SymbolIndex

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impl Ord for UnpackedIndex

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impl Ord for ValType

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impl Ord for ValType

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impl Ord for ValidatorId

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impl<'a> Ord for Component<'a>

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impl<'a> Ord for Prefix<'a>

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impl<'a> Ord for Location<'a>

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impl<'a> Ord for Metadata<'a>

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impl<'a> Ord for MetadataBuilder<'a>

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impl<'a> Ord for DependencyName<'a>

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impl<'a> Ord for HashName<'a>

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impl<'a> Ord for InterfaceName<'a>

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impl<'a> Ord for ResourceFunc<'a>

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impl<'a> Ord for UrlName<'a>

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impl<A> Ord for &A
where A: Ord + ?Sized,

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impl<A> Ord for &mut A
where A: Ord + ?Sized,

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impl<A> Ord for SmallVec<A>
where A: Array, <A as Array>::Item: Ord,

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impl<B> Ord for Cow<'_, B>
where B: Ord + ToOwned + ?Sized,

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impl<Dyn> Ord for DynMetadata<Dyn>
where Dyn: ?Sized,

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impl<E> Ord for I16<E>
where E: Ord + Endian,

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impl<E> Ord for I16Bytes<E>
where E: Ord + Endian,

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impl<E> Ord for I32<E>
where E: Ord + Endian,

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impl<E> Ord for I32Bytes<E>
where E: Ord + Endian,

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impl<E> Ord for I64<E>
where E: Ord + Endian,

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impl<E> Ord for I64Bytes<E>
where E: Ord + Endian,

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impl<E> Ord for U16<E>
where E: Ord + Endian,

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impl<E> Ord for U16Bytes<E>
where E: Ord + Endian,

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impl<E> Ord for U32<E>
where E: Ord + Endian,

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impl<E> Ord for U32Bytes<E>
where E: Ord + Endian,

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impl<E> Ord for U64<E>
where E: Ord + Endian,

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impl<E> Ord for U64Bytes<E>
where E: Ord + Endian,

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impl<F> Ord for F
where F: FnPtr,

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impl<K, V> Ord for Slice<K, V>
where K: Ord, V: Ord,

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impl<K, V, A> Ord for BTreeMap<K, V, A>
where K: Ord, V: Ord, A: Allocator + Clone,

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impl<Ptr> Ord for Pin<Ptr>
where Ptr: Deref, <Ptr as Deref>::Target: Ord,

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impl<T> Ord for Option<T>
where T: Ord,

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impl<T> Ord for Poll<T>
where T: Ord,

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impl<T> Ord for *const T
where T: ?Sized,

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impl<T> Ord for *mut T
where T: ?Sized,

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impl<T> Ord for [T]
where T: Ord,

Implements comparison of slices lexicographically.

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impl<T> Ord for (Tโ‚, Tโ‚‚, โ€ฆ, Tโ‚™)
where T: Ord + ?Sized,

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

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impl<T> Ord for PackedOption<T>
where T: Ord + ReservedValue,

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impl<T> Ord for Cell<T>
where T: Ord + Copy,

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impl<T> Ord for RefCell<T>
where T: Ord + ?Sized,

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impl<T> Ord for Reverse<T>
where T: Ord,

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impl<T> Ord for PhantomData<T>
where T: ?Sized,

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impl<T> Ord for ManuallyDrop<T>
where T: Ord + ?Sized,

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impl<T> Ord for NonZero<T>

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impl<T> Ord for Saturating<T>
where T: Ord,

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impl<T> Ord for Wrapping<T>
where T: Ord,

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impl<T> Ord for NonNull<T>
where T: ?Sized,

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impl<T> Ord for DebugInfoOffset<T>
where T: Ord,

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impl<T> Ord for DebugTypesOffset<T>
where T: Ord,

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impl<T> Ord for Slice<T>
where T: Ord,

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impl<T> Ord for Unalign<T>
where T: Unaligned + Ord,

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impl<T> Ord for UnitOffset<T>
where T: Ord,

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impl<T> Ord for UnitSectionOffset<T>
where T: Ord,

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impl<T, A> Ord for Box<T, A>
where T: Ord + ?Sized, A: Allocator,

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impl<T, A> Ord for Vec<T, A>
where T: Ord, A: Allocator,

Implements ordering of vectors, lexicographically.

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impl<T, A> Ord for BTreeSet<T, A>
where T: Ord, A: Allocator + Clone,

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impl<T, A> Ord for LinkedList<T, A>
where T: Ord, A: Allocator,

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impl<T, A> Ord for VecDeque<T, A>
where T: Ord, A: Allocator,

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impl<T, A> Ord for Rc<T, A>
where T: Ord + ?Sized, A: Allocator,

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impl<T, A> Ord for Arc<T, A>
where T: Ord + ?Sized, A: Allocator,

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impl<T, B> Ord for Ref<B, [T]>
where B: ByteSlice, T: FromBytes + Ord,

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impl<T, B> Ord for Ref<B, T>
where B: ByteSlice, T: FromBytes + Ord,

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impl<T, E> Ord for Result<T, E>
where T: Ord, E: Ord,

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impl<T, const N: usize> Ord for [T; N]
where T: Ord,

Implements comparison of arrays lexicographically.

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impl<T, const N: usize> Ord for Simd<T, N>

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impl<Y, R> Ord for CoroutineState<Y, R>
where Y: Ord, R: Ord,