Java has JSR 354 for money [1]. There is also a reference implementation [2]. So there is official support for money in Java.
[1] https://jcp.org/en/jsr/detail?id=354 [2] https://javamoney.github.io/
[1] https://jcp.org/en/jsr/detail?id=354 [2] https://javamoney.github.io/
Money ask = 2.1M USD;
What I don't see with the Java JSR is how exchange rate services are integrated (if at all?). In the best of worlds, as with manifold's units I could write.
Money deposit = 300 USD + 500 EUR;
Where internally the deposit automatically maintains the amounts separately and uses exchange rates only for spot display/calc, transfer, etc.
1. https://github.com/manifold-systems/manifold/tree/master/man...
USD rent = 2000
EUR salary = 6000.53
USD disposableIncome = salary - rent
Then:
disposableIncome.toDecimal()
disposableIncome.toInteger()
disposableIncome.toString()
USD interest = disposableIncome.compoundInterest(startDate, endDate, apy)
USD tip = billTotal.tip(percentage)
USD and EUR would inherit from Money
Not sure how to implement it, might be a JVM magic thing.
Money cost = 25M USD;
cost += 12M EUR;
display(cost.to(EUR));
> just as meter is a unit type of Length
The difference is that length units are fixed, but exchange rates are constantly changing.
Right. As I mentioned earlier exchange rate services would need to be integrated into the API.
Also, exchange rate services would not be needed until a conversion is necessary. For instance, when adding money of different currencies internally the Money type maintains currencies separately, subtotals for USD, EUR, etc. are managed. If at a later time the sum of Money should be displayed, deposited, etc. as a single currency, only then is an exchange service involved.
Feels like it should be
Money<USD> ask = 2.1M USD;
For instance, physical dimensions store values as SI units, regardless of supplied unit, but retain the supplied unit type as a display hint.
Here, the Length dimension illustrates working with amounts of any unit.
Length orbit = 250 mi;
Length moon = 238000 km;
Length landing = moon + orbit;
display(landing); // prints 148,136.344 mi
display(landing.to(km)); // prints 238,402.336 km
// where
display(landing.to(mi) == landing.to(km)); // prints true
// perhaps a better example
Rate rate = 1.41 km/s;
Time duration = 76 hours;
Length distance = rate * duration;
// make your own unit constants
RateUnit kps = km/s;
rate = 1.41 kps;
You can play with the manifold-science[1] project, it implements the complete SI physical dimensions and many derived dimensions along with comprehensive operator overloading[2] support etc. to make working with and reading code using quantities more productive in Java.
1. https://github.com/manifold-systems/manifold/tree/master/man...
2. https://github.com/manifold-systems/manifold/tree/master/man...
Using Java library will limit your program only to jvm platform. Using a kotlin library like this one (given it's written in pure kotlin and doesn't uses any jvm platforms specifics) will allow you to build it to whatever target kmp supports (macosx, ios, android, js, mingw...)
Plenty of languages (also Java with Graal, TeaVM, J2CL, etc.) can also target these platforms.
But as with all these languages targeting these platforms (including Kotlin) you are going to have to call platform specific API if you want to do anything useful. There are also platforms specific limitations which means certain stuff which you can do in the language doesn't work on those platforms.