What is the intended value-type contract for convert/2?

[DamienFriot]

Hi,
Thanks for all updates. I started replacing CLDR in my app for testing and got a few more points.
The first one:

A question rather than a bug report. On main @ a28da2f, convert/2 preserves Decimal values (thanks for that fix in rc.3) but returns floats for integer-valued units:

{:ok, u} = Localize.Unit.new(1, "tonne")             # value: 1 (integer)
{:ok, c} = Localize.Unit.convert(u, "kilogram")
c.value                                               #=> 1000.0 (float)

{:ok, u2} = Localize.Unit.new(Decimal.new(1), "tonne")
{:ok, c2} = Localize.Unit.convert(u2, "kilogram")
c2.value                                              #=> Decimal — exact

I can see the case for floats in a display-oriented library but the Decimal fix suggests a different principle: input type governs output type. What is the intented value-type contract?

Thank you in advance

[kipcole9]

The basic type contract is: Decimal in -> Decimal out because Decimal can represent an exact value. Int/Float in -> Float out because integer's simply can't represent the domain. If it was Int in -> Int out then converting 1 Km to miles would return 1 mile and that would be very misleading and unexpected. Therfore, if exact values are required, use Decimal values units.

I'm updating the docs to be clearer about the contract - its a very good question.

[kipcole9]

Doc commit 3b535b1 is now pushed.