pub trait ConstCmp {
type Kind;
}Expand description
Marker trait for types that implement the const comparison methods.
§Implementors
Types that implement this trait are also expected to implement at least one of these inherent methods:
use std::cmp::Ordering;
const fn const_eq(&self, other: &Self) -> bool
const fn const_cmp(&self, other: &Self) -> Ordering
§Coercions
The Kind associated type
is used in the IsAConstCmp marker type
to automatically wrap types in CmpWrapper if they’re from the standard library,
otherwise leaving them unwrapped.
§Example
§Manual Implementation
use konst::{
cmp::{ConstCmp, IsNotStdKind},
const_cmp, const_eq, try_equal,
};
use std::cmp::Ordering;
struct MyType {
x: &'static str,
y: &'static [u16],
}
impl ConstCmp for MyType {
type Kind = IsNotStdKind;
}
impl MyType {
pub const fn const_eq(&self, other: &Self) -> bool {
const_eq!(self.x, other.x) &&
const_eq!(self.y, other.y)
}
pub const fn const_cmp(&self, other: &Self) -> Ordering {
try_equal!(const_cmp!(self.x, other.x));
try_equal!(const_cmp!(self.y, other.y))
}
}
const _: () = {
let foo = MyType{x: "hello", y: &[3, 5, 8, 13]};
let bar = MyType{x: "world", y: &[3, 5, 8, 13]};
assert!(matches!(const_cmp!(foo, foo), Ordering::Equal));
assert!(matches!(const_cmp!(foo, bar), Ordering::Less));
assert!(matches!(const_cmp!(bar, foo), Ordering::Greater));
assert!(const_eq!(foo, foo));
assert!(!const_eq!(foo, bar));
};§ìmpl_cmp-based Implementation
You can use impl_cmp to implement this trait,
as well as define the same methods for
multiple implementations with different type arguments.
use konst::{const_cmp, const_eq, impl_cmp, try_equal};
use std::cmp::Ordering;
struct MyType<'a, T> {
x: &'a str,
y: &'a [T],
}
impl_cmp!{
// The comparison functions are only implemented for these types.
impl['a] MyType<'a, bool>;
impl['a] MyType<'a, u16>;
impl['a] MyType<'a, &'static str>;
pub const fn const_eq(&self, other: &Self) -> bool {
const_eq!(self.x, other.x) &&
const_eq!(self.y, other.y)
}
pub const fn const_cmp(&self, other: &Self) -> Ordering {
try_equal!(const_cmp!(self.x, other.x));
try_equal!(const_cmp!(self.y, other.y))
}
}
const _: () = {
let foo = MyType{x: "hello", y: &[3, 5, 8, 13]};
let bar = MyType{x: "world", y: &[3, 5, 8, 13]};
assert!(matches!(const_cmp!(foo, foo), Ordering::Equal));
assert!(matches!(const_cmp!(foo, bar), Ordering::Less));
assert!(matches!(const_cmp!(bar, foo), Ordering::Greater));
assert!(const_eq!(foo, foo));
assert!(!const_eq!(foo, bar));
};
const _: () = {
let foo = MyType{x: "hello", y: &[false]};
let bar = MyType{x: "hello", y: &[true]};
assert!(matches!(const_cmp!(foo, foo), Ordering::Equal));
assert!(matches!(const_cmp!(foo, bar), Ordering::Less));
assert!(matches!(const_cmp!(bar, foo), Ordering::Greater));
assert!(const_eq!(foo, foo));
assert!(!const_eq!(foo, bar));
};
Required Associated Types§
Sourcetype Kind
type Kind
What kind of type this is, this can be one of:
-
IsStdKind: A standard library type. -
IsRefKind: A reference type. -
IsNotStdKind: A type that is not from the standard library.