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by ynik
813 days ago
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Your software will still "lose" cents if you use integers, for operations such as dividing a bill (e.g. divide by 3), or applying 3% APR in monthly increments. The goal is not to avoid rounding errors (which would be quite difficult when the true account value can be an irrational number, as with 3% APR compounding monthly), but to have the exact same rounding errors that are prescribed by the accounting practices. Which may vary depending on legislation. A decimal floating point is usually a better starting point than integers are. |
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Which is why passing around ints is not the solution. And why I specifically mention Domain Models and/or Value Object.
A domain model would throw an exeption or otherwise dissalow certain divisions for example. What I often do, is something like `expense.amount.divide_over(3, leftover_to_last)` or `savings.balance_at(today).percentage_of(3.1337)`.
Sometimes, in simpler setups and when the language allows, I'll re-implement operators like *, / and even + and -. But when actual business logic is needed, I'll avoid these and implement actual domain methods that use the language the business uses.
But never, ever, do I allow just math-ing over the inner values.
So, I disagree: Both decimal floating point and integers are just as "bad". Maybe for the inner values in the domain model or value object, they are fine, but often there integers are a slightly better starting point because they make rounding and leftovers very explicit.