Function boundary_distance 

pub fn boundary_distance(
    a: &ExactBRep,
    b: &ExactBRep,
    accuracy: f64,
    tolerance: Tolerance,
) -> Result<DistanceBounds, ExactMeasureError>

Distance between the boundaries of a and b, to within accuracy.

An accuracy below the rounding floor settles at the floor and is never reported as met: the interval returned shows its width (see “Rounding” in the module docs).

Errors

A face whose domain cannot be bounded (an unbounded surface trimmed by a pcurve family the domain classifier does not split), an evaluation failure, or boundaries with no boundable edge or face.