Enum Cardinality 

#[non_exhaustive]
#[repr(i32)]
pub enum Cardinality {
    Unspecified = 0,
    Low = 1,
    Medium = 2,
    High = 3,
    Unbounded = 4,
}

Bound on the number of distinct values a field admits at runtime.

Drives lint L001 (LABEL fields must be Low or Medium) and L005 (enum variant count must fit the cap). See 10-data-model.md § 4.

Variants (Non-exhaustive)

Non-exhaustive enums could have additional variants added in future. Therefore, when matching against variants of non-exhaustive enums, an extra wildcard arm must be added to account for any future variants.

Unspecified = 0

Never appears in a well-formed schema.

Low = 1

< 10 distinct values (status, boolean).

Medium = 2

< 10_000 distinct values (route, tenant).

High = 3

< 1_000_000 distinct values (user_id) — illegal for LABEL.

Unbounded = 4

Open / unbounded — illegal for LABEL and MEASUREMENT.

Implementations

impl Cardinality

pub const fn as_str(self) -> &'static str

Stable string label.

pub const fn cap(self) -> u64

Numeric cap: the maximum distinct value count permitted at this level. Returns u64::MAX for Unbounded. Used by lint L005 (variant count).

Unspecified returns 0 — a schema that did not declare cardinality should fail the cap check.

pub const fn is_label_compatible(self) -> bool

True if this cardinality is permitted on a FieldKind::Label field. Labels become metric/span dimensions; only Low and Medium are safe.

pub const fn is_measurement_compatible(self) -> bool

True if this cardinality is permitted on a FieldKind::Measurement field. Unbounded is illegal — measurement values come from the numeric type, not from the cardinality.

Trait Implementations

impl Clone for Cardinality

fn clone(&self) -> Cardinality

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Debug for Cardinality

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

Formats the value using the given formatter.

impl Default for Cardinality

fn default() -> Cardinality

Returns the “default value” for a type.

impl<'de> Deserialize<'de> for Cardinality

fn deserialize<__D>(__deserializer: __D) -> Result<Self, __D::Error>

where __D: Deserializer<'de>,

Deserialize this value from the given Serde deserializer.

impl Enumeration for Cardinality

fn from_i32(value: i32) -> Option<Self>

Convert from an i32 wire value to the enum.

fn to_i32(&self) -> i32

Convert the enum to its i32 wire value.

fn proto_name(&self) -> &'static str

The name of this enum variant as it appears in the .proto file.

fn from_proto_name(name: &str) -> Option<Self>

Look up a variant by its protobuf name string.

fn values() -> &'static [Self]

All known variants of this enum, in proto declaration order.

impl FromStr for Cardinality

type Err = UnknownVariant

The associated error which can be returned from parsing.

fn from_str(s: &str) -> Result<Self, Self::Err>

Parses a string s to return a value of this type.

impl Hash for Cardinality

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 Cardinality

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

Tests for self and other values to be equal, and is used by ==.

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

Tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.

impl Serialize for Cardinality

fn serialize<__S>(&self, __serializer: __S) -> Result<__S::Ok, __S::Error>

where __S: Serializer,

Serialize this value into the given Serde serializer.

impl Copy for Cardinality

impl Eq for Cardinality

impl StructuralPartialEq for Cardinality