ExchangeRate

A rate between two currencies at an instant: one from is rate of to, written GBP/EUR 1.17 2026-10-18T09:00:00Z. An app holds one it was given; money.convert applies it.

Money and banking; not ordered; since Jadpo 0.1.0.

Make one

Build one from its fields, ExchangeRate { from: ... to: ... rate: ... }.

text.parse(raw, as: ExchangeRate) reads one from its text; text that isn't one at all fails malformed, such as GBP/EUR 1.17, GBP-EUR 1.17 2026-10-18T09:00:00Z or GBP/XYZ 1.17 2026-10-18T09:00:00Z.

Fields

Text, JSON and storage

text.from writes its canonical text, the one form text.parse reads back. JSON sends an object of its parts.

It is stored in 4 columns, each named for the field, _ and its suffix. This is EUR/JPY 162.4031 2026-10-18T09:30:00Z:

Shown to people

text.format(value, locale:) shows it to people in their locale.

With locale: Locale.en_gb:

Operations

• money.convert(value: Money, rate: ExchangeRate) -> Money: value in rate's to currency, from its from one: the major units times rate.rate, rounded half to even to a minor unit, so £10.50 at a GBP/EUR rate of 1.17 is €12.28. It fails with currency_mismatch when value isn't in rate.from, unless that is known: an inverted rate is then a compile error. The rate is one the app holds; nothing here fetches one.

Like every standard type, it also has the contract's own operations: text.parse, text.from, text.format, json.read, json.write and ==. It isn't ordered, so < and sorting don't take it. Every standard type meets one contract says how they work.