How should be managed unknown units with conversion ?

[tpoisseau]

https://en.wikipedia.org/wiki/Hectare#Are

Let say runtime known meter unit, be we want work with Are (1a = 100m2) and this unit is not known by the runtime.

Should this proposal allow to add custom units and describe possible conversions ?

API Idea (pseudocode):

Measure.addUnit({
  symbol: 'a',
  name: 'are',
  kind: {type: 'distance', exponent: 2} // surface
  conversions: [
    {
      type: 'distance',
      exponent: 2,
      unit: 'meter',
      convertTo: (ares: number) => ares * 100,
      convertFrom: (m2: number) => m2 / 100,
    }
  ],
});

const measureAre = new Measure(1, {unit: 'are'});
const measureM2 = measureAre.convertTo('meter');
// Measure { value: 100, unit: 'meter', exponent: 2}