[xlii]

Quick browse over Stripe API (i.e. not a simplistic payment provider) will show exactly otherwise.

Metrics/durations/convexity/vega aren't monetary value, these are calculation values and I'm fine with them being whatever. If you're calculating averages to make decisions based on this I don't care if you're counting dolars or tomatoes.

Monetary value is $4.50 and it's representation of actual money passed through system. In practice this value is almost never undergoing any operations except for addition and subtraction. Any multiplication/divison etc. is left to specialized systems that return results wrapped in 800 pages of standarization documents, regulations and so on; systems where term "bit flip" is not a joke, but a risk.

As I wrote fintech != fintech, and I know many organizations aren't at that level of scrutiny, but a huge domain of people dealing with others' people money know that charging someone 1 cent too much is a tens of thousands of problems coming their way.

[fauigerzigerk]

What's your preferred solution to dealing with FX conversions?

My issue with using integers everywhere is that FX conversions (or other rates) always come into play, and at that point I'm forced to use something else anyway (e.g. arbitrary precision decimals).

[xlii]

I never had to deal with that. At one place it was so complicated that specialized system took reconciliation over (it got baggage full of context data including exchange agreement details, with boundaries and time-regions plan).

In not-a-fintech we just went with doubles and rounded up (worst case - we get a cent more of a customer).

Though if I had to design today for that, I'd look for non-string serializable decimal, so not "10.123 == (10, 123)" but more like (10123, 3) and serialize in JSON as a value and precision separately.

Yet that's only cause I saw Decimal(10,123) sent in JSON as "10.123" which JSON reader red as 10.122 float and inserted to "1012" to database.

[nly]

I worked on a trading system dealing with transaction limits expressed in USD but trading in many currencies.

FX rates and prices were expressed in fixed point because it was more efficient to handle in FPGA. A lot of thought went in to making the system accurate enough based on real FX rates while falling on the right side of the limit