Formulas in which we divide by x throws an exception when x = 0

[aidbal]

Hey @angularsen, I have recently published a pr to create a new Fuel Efficiency unit (#703).

In one of the formulas, there is a division by zero. It happens, that sometimes in our code we have the following call FuelEfficiency.ToUnit(FuelEfficiencyUnit) which throws an exception.

After inspecting the generated code, I have found that nowhere it checks for division by zero, thus the formula 100/x becomes 100/0 and it throws an exception.

I am not sure how propose fixes for this problem, that's why I am writing it here. Right now, I have created an extension method, which first, checks for initial value, and then, if it's non-zero, it calls it's base method.

One more thing, you cannot apply check by zero to all values, because 0 Celsius is not 0 Kelvins and vice versa.

[angularsen]

Hi, that sounds about right. There are no zero checks, because that would be hard to do in a generic manner for all the different functions.

So I tried this:

// ArgumentException: PositiveInfinity or NegativeInfinity is not a valid number.Parameter name: value
FuelEfficiency.FromLitersPer100Kilometers(0).ToUnit(FuelEfficiencyUnit.KilometerPerLiter)

// OK
FuelEfficiency.FromLitersPer100Kilometers(1).ToUnit(FuelEfficiencyUnit.KilometerPerLiter)

Isn't this kind of the correct behavior, though?

Zero liters per 100 kilometers is infinite kilometers per liter. Did you perhaps expect the .Value property to be double.PositiveInfinity? If so, that is by design unfortunately #502.

For debatable reasons, a handful of quantities use decimal backing value type to support conversions between very small and very large units. That numeric type does not support NaN or Infinity, so we decided to not support those in any quantities for consistency.

We do have some ideas on how to fix this with generics #666 and allowing the consumer to choose between float, double and decimal, but no one is actively working on it yet. We could also consider allowing Infinity and NaN for the majority of quantities that use double, but I think I would rather invest time towards generics maybe.

Did that answer your question?

[aidbal]

Actually you are quite right. 0 liters/100km means infinitely kilometers/liter. But I think that depends on our agreement. In practice, we have a parameter for such a type. And if it's unset, it has value of 0. So no matter what measurement system you use, it should be 0. That means 0 L/100km should be 0 km/L.

What are your ideas on this? Maybe it's just our business logic. And if so, as I said, we have adapted to it through extension methods.

[angularsen]

Could you take FuelEfficiency? as parameter and have an agreement that says it is null if it is unset? It seems ambiguous to let 0 mean both unset and the actual value 0.

[aidbal]

Yeah sure, we will adapt it to our business needs. I opened this issue so others wouldn't encounter this problem.