Enum CapKind 

pub enum CapKind {
    Eq,
    Ord,
    Hash,
    HashStable,
    Numeric,
}

One structural property a type either has or does not (§5.4, §5.5).

The five are not independent; the two hash-shaped ones are a pair, see CapKind::HashStable.

Variants

Eq

Comparable with == / != (§5.5). Scalars and Unit are; a composite is iff every component is; functions never are.

Ord

Has a total order — usable with </>, in a heap, or as a sort key (§5.4 SupportsOrd, ADR-045). The orderable types are exactly the scalars whose descriptors carry a compare callback.

Hash

Hashable: the runtime can compute a structural hash of the value. This is CapKind::Eq’s companion — the descriptor’s hash and equals callbacks are defined together — and on its own it is not enough to be a key.

HashStable

Hashable and immutable, which is what a Map key or Set element must be (D4).

A Vec is hashable: the runtime can hash its current contents. It is not stably hashable, because key.push(2) after table.insert(key, v) moves the entry’s hash without moving the entry, and the value can no longer be found. Python rejects list/dict/set as keys for exactly this reason; Rust permits HashMap<Vec<i32>, V> only because the borrow checker makes mutating a held key impossible, and Praxis has var mutation and no borrow checker.

The rule is mutability, not container-ness: scalars, Text, tuples, records and enums are stable structurally — a tuple is a key iff every component is — and the eight mutable collections are not.

Numeric

Numeric: admits +, -, *, /, unary minus, and the numeric sinks (sum, product). Int, UInt, Byte and Float are; nothing else is. % is narrower still and is not this capability.

Implementations

impl CapKind

pub const ALL: &'static [CapKind]

Every capability, for exhaustive sweeps (agreement tests, tables).

Trait Implementations

impl Clone for CapKind

fn clone(&self) -> CapKind

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Copy for CapKind

impl Debug for CapKind

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl Eq for CapKind

impl Hash for CapKind

fn hash<__H: Hasher>(&self, state: &mut __H)

Feeds this value into the given Hasher.

fn hash_slice<H>(data: &[Self], state: &mut H)

where H: Hasher, Self: Sized,

Feeds a slice of this type into the given Hasher.

impl PartialEq for CapKind

fn eq(&self, other: &CapKind) -> bool

Equality operator ==.

fn ne(&self, other: &Rhs) -> bool

Inequality operator !=.

impl StructuralPartialEq for CapKind