Enum Scale 

#[non_exhaustive]
pub enum Scale {
    Ratio,
    #[non_exhaustive]
    Interval {
        min: f64,
        max: f64,
        unit: f64,
    },
}

The measurement scale of a metric’s value: which arithmetic on it means anything (issue #1621).

Stevens’ classification of measurement scales (On the Theory of Scales of Measurement, Science 103, 1946) is the reason this is a separate axis from Direction. On a ratio scale zero means “none of it”, so value / limit and “N percent worse” are meaningful: 30 branches is twice 15. On an interval scale the zero is arbitrary, so only differences are meaningful: a Maintainability Index of -10 is not “twice as bad” as -5, and a drop from 0.001 to -0.0097 is a hundredth of a point, not a 1069 % fall. Every surface that ranks, scales or reports a change reads this instead of assuming ratio arithmetic; Threshold is where that arithmetic lives.

#[non_exhaustive], as is the Interval variant, so a scale or a field can be added in a minor release. Match with a wildcard arm and Interval { unit, .. }.

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.

Ratio

True zero, values >= 0: every count and count-derived metric (cyclomatic, halstead.*, loc.*, …). Severity is the plain value / limit ratio and a change is a percentage.

#[non_exhaustive]

Interval

Arbitrary zero: the Maintainability Index family. Only differences are meaningful, so severity and change are measured in multiples of unit.

Fields

Non-exhaustive enum variants could have additional fields added in future. Therefore, non-exhaustive enum variants cannot be constructed in external crates and cannot be matched against.

min: f64

Smallest value the metric can take (may be -INFINITY).

max: f64

Largest value the metric can take (may be INFINITY).

unit: f64

One step of badness, in the metric’s own points: the distance that plays the role a Ratio metric’s limit plays in severity, soft-tier scaling and drift. Always finite and positive.

Trait Implementations

impl Clone for Scale

fn clone(&self) -> Self

Returns a duplicate of the value.

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

Performs copy-assignment from source.

impl Copy for Scale

impl Debug for Scale

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

Formats the value using the given formatter.

impl PartialEq for Scale

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

Equality operator ==.

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

Inequality operator !=.

impl StructuralPartialEq for Scale