Trait gstd::prelude::Ord

1.0.0 · source ·

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 + PartialOrd { ... }
}

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.

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

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.

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, 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 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.

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§

source

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

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§

1.21.0 · source

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

Compares and returns the maximum of two values.

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

Examples

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

1.21.0 · source

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

Compares and returns the minimum of two values.

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

Examples

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

1.50.0 · source

fn clamp(self, min: Self, max: Self) -> Self
where Self: Sized + PartialOrd,

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

Object Safety§

This trait is not object safe.

Trait gstd::prelude::Ord

Required Methods§

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

Provided Methods§

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

fn min(self, other: Self) -> Selfwhere Self: Sized,

fn clamp(self, min: Self, max: Self) -> Selfwhere Self: Sized + PartialOrd,

Object Safety§

Implementors§

impl Ord for ErrorReplyReason

impl Ord for ExecutionError

impl Ord for ExtError

impl Ord for MemoryError

impl Ord for MessageError

impl Ord for ProgramRentError

impl Ord for ReplyCode

impl Ord for ReservationError

impl Ord for SignalCode

impl Ord for SimpleExecutionError

impl Ord for SimpleProgramCreationError

impl Ord for SuccessReplyReason

impl Ord for AsciiChar

impl Ord for Ordering

impl Ord for Infallible

impl Ord for IpAddr

impl Ord for SocketAddr

impl Ord for MetaForm

impl Ord for PortableForm

impl Ord for TypeDefPrimitive

impl Ord for bool

impl Ord for char

impl Ord for i8

impl Ord for i16

impl Ord for i32

impl Ord for i64

impl Ord for i128

impl Ord for isize

impl Ord for !

impl Ord for str

impl Ord for u8

impl Ord for u16

impl Ord for u32

impl Ord for u64

impl Ord for u128

impl Ord for ()

impl Ord for usize

impl Ord for SyscallError

impl Ord for gstd::ActorId

impl Ord for gstd::CodeId

impl Ord for gstd::MessageId

impl Ord for Percent

impl Ord for gstd::ReservationId

impl Ord for MetaType

impl Ord for TypeId

impl Ord for CStr

impl Ord for CString

impl Ord for Error

impl Ord for CpuidResult

impl Ord for Ipv4Addr

impl Ord for Ipv6Addr

impl Ord for SocketAddrV4

impl Ord for SocketAddrV6

impl Ord for gcore::general::ActorId

impl Ord for gcore::general::CodeId

impl Ord for gcore::general::MessageId

impl Ord for gcore::general::ReservationId

impl Ord for H128

impl Ord for H160

impl Ord for H256

impl Ord for H384

impl Ord for H512

impl Ord for H768

impl Ord for U128

impl Ord for U256

impl Ord for U512

impl Ord for PhantomPinned

impl Ord for NonZeroI8

impl Ord for NonZeroI16

impl Ord for NonZeroI32

impl Ord for NonZeroI64

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 + PartialOrd,

impl<'a, T> Ord for Symbol<'a, T>
where T: Ord + 'a,

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

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

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

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

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

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

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

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

impl<T> Ord for TypeDef<T>
where T: Ord + Form,

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

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

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

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

impl<T> Ord for (T₁, T₂, …, Tₙ)
where T: Ord + ?Sized,

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

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

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

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

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

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

impl<T> Ord for TypeDefComposite<T>
where T: Ord + Form,

impl<T> Ord for Field<T>
where T: Ord + Form, <T as Form>::String: Ord, <T as Form>::Type: Ord,

impl<T> Ord for Path<T>
where T: Ord + Form, <T as Form>::String: Ord,

impl<T> Ord for Type<T>
where T: Ord + Form, <T as Form>::String: Ord,

impl<T> Ord for TypeDefArray<T>
where T: Ord + Form, <T as Form>::Type: Ord,

impl<T> Ord for TypeDefBitSequence<T>
where T: Ord + Form, <T as Form>::Type: Ord,

impl<T> Ord for TypeDefCompact<T>
where T: Ord + Form, <T as Form>::Type: Ord,

impl<T> Ord for TypeDefSequence<T>
where T: Ord + Form, <T as Form>::Type: Ord,

impl<T> Ord for TypeDefTuple<T>
where T: Ord + Form, <T as Form>::Type: Ord,

impl<T> Ord for TypeParameter<T>
where T: Ord + Form, <T as Form>::String: Ord, <T as Form>::Type: Ord,

impl<T> Ord for TypeDefVariant<T>
where T: Ord + Form,

impl<T> Ord for Variant<T>
where T: Ord + Form, <T as Form>::String: Ord,

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

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

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

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

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

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

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