Enum CurveMeasure

#[non_exhaustive]
pub enum CurveMeasure {
    Distance(Scalar),
    Parameter(Scalar),
}

Where along a curve to evaluate, and by WHICH method of measurement.

Two different quantities are routinely written into exchange files for the same purpose, and they are not interchangeable:

• a LENGTH from the start of the curve, and
• a dimensionless native PARAMETER, which is not a distance at all.

IFC4x3 makes the choice explicit in the file (IfcCurveMeasureSelect, either IfcNonNegativeLengthMeasure or IfcParameterValue), and STEP carries the same distinction. A consumer maps the authored value to this enum ONCE and passes it through; it never has to decide which evaluator to call.

Why this is a value and not two method names: with separate *_at_parameter methods the caller still branches, and a caller that branches can branch wrongly. Passing 1.5 as a distance to a circle authored in radians places an object 1.5 m along a curve where the author meant about 86 degrees around it – wrong, finite, and plausible, which is the worst combination. Carrying the method of measurement in the value makes that mistake unrepresentable.

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.

Distance(Scalar)

A length from the start of the curve.

Interpreted in the provider’s DistanceConvention for that curve, which is why the convention must be consulted before trusting it.

Parameter(Scalar)

The curve’s own parameter: an angle for a circle, a knot value for a spline, arc length for an intrinsic curve.

Meaningful for every curve family, including those whose arc length has no closed form, so this route stays available where Distance is refused.

Implementations

impl CurveMeasure

pub fn value(self) -> Scalar

The carried number, whichever method of measurement it uses.

For validity checks such as finiteness that apply to both.

pub fn is_distance(self) -> bool

Whether this is a length rather than a native parameter.

Trait Implementations

impl Clone for CurveMeasure

fn clone(&self) -> CurveMeasure

Returns a copy of the value.

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

Performs copy-assignment from source.

impl Debug for CurveMeasure

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

Formats the value using the given formatter.

impl PartialEq for CurveMeasure

fn eq(&self, other: &CurveMeasure) -> 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 Copy for CurveMeasure

impl StructuralPartialEq for CurveMeasure