Trait druid::piet::cairo::glib::bitflags::_core::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<U> and U: PartialOrd<V> then U: PartialOrd<T> and T: PartialOrd<V>.

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);

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

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

Implements comparison of vectors, lexicographically.

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<TabsTransition> for TabsTransition

impl PartialOrd<NormalForm> for NormalForm

impl PartialOrd<Antialias> for Antialias

impl PartialOrd<Content> for Content

impl PartialOrd<DeviceType> for druid::piet::cairo::DeviceType

impl PartialOrd<Extend> for Extend

impl PartialOrd<FillRule> for FillRule

impl PartialOrd<Filter> for Filter

impl PartialOrd<FontSlant> for FontSlant

impl PartialOrd<FontType> for FontType

impl PartialOrd<FontWeight> for FontWeight

impl PartialOrd<HintMetrics> for HintMetrics

impl PartialOrd<HintStyle> for HintStyle

impl PartialOrd<LineCap> for LineCap

impl PartialOrd<LineJoin> for LineJoin

impl PartialOrd<MeshCorner> for MeshCorner

impl PartialOrd<Operator> for Operator

impl PartialOrd<PathDataType> for PathDataType

impl PartialOrd<PatternType> for PatternType

impl PartialOrd<SubpixelOrder> for SubpixelOrder

impl PartialOrd<TextClusterFlags> for TextClusterFlags

impl PartialOrd<ChecksumType> for ChecksumType

impl PartialOrd<ConvertError> for ConvertError

impl PartialOrd<DateMonth> for DateMonth

impl PartialOrd<DateWeekday> for DateWeekday

impl PartialOrd<FileError> for FileError

impl PartialOrd<KeyFileError> for KeyFileError

impl PartialOrd<LogWriterOutput> for LogWriterOutput

impl PartialOrd<MarkupError> for MarkupError

impl PartialOrd<OptionArg> for OptionArg

impl PartialOrd<SeekType> for SeekType

impl PartialOrd<TimeType> for TimeType

impl PartialOrd<UnicodeScript> for UnicodeScript

impl PartialOrd<VariantClass> for VariantClass

impl PartialOrd<Infallible> for Infallible

impl PartialOrd<IpAddr> for IpAddr

impl PartialOrd<IpAddr> for Ipv4Addr

impl PartialOrd<IpAddr> for Ipv6Addr

impl PartialOrd<SocketAddr> for SocketAddr

impl PartialOrd<Which> for Which

impl PartialOrd<Ordering> for Ordering

impl PartialOrd<ErrorKind> for ErrorKind

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<BlendMode> for BlendMode

impl PartialOrd<bool> for bool

impl PartialOrd<char> for char

impl PartialOrd<f32> for f32

impl PartialOrd<f64> for f64

impl PartialOrd<i8> for i8

impl PartialOrd<i16> for i16

impl PartialOrd<i32> for i32

impl PartialOrd<i64> for i64

impl PartialOrd<i64> for ILong

impl PartialOrd<i128> for i128

impl PartialOrd<isize> for isize

impl PartialOrd<!> for !

impl PartialOrd<str> for str

impl PartialOrd<str> for GStr

impl PartialOrd<str> for GString

impl PartialOrd<str> for GStringBuilder

impl PartialOrd<str> for OsStr

impl PartialOrd<str> for OsString

impl PartialOrd<u8> for u8

impl PartialOrd<u16> for u16

impl PartialOrd<u32> for u32

impl PartialOrd<u64> for u64

impl PartialOrd<u64> for ULong

impl PartialOrd<u128> for u128