> Can you confidently say that $100>¥10 in an offline environment?
Money is never converted. It is exchanged. Trying to solve this is like trying to solve the question "Is "100 USD" > "1 LAPTOP".
When you turn 100 USD into 90 EUR, you didn't convert it. You exchanged it. You bought EUR, at a price given to you by someone or something exchanging it. This could be a bank, a well-established currency office, or some dude on the street. There is no real difference between all three of those: The third party gave you a price, and now has more USD and less EUR, whereas you have more EUR and less USD.
There are various entities publishing standardized average rates which are calculated after the day closes, based on a variety of datapoints they have access to. Those are often used in eg. accounting, to establish the "real" value of something you bought in a currency you don't often use, but it's not true conversion.
If you have, as a datatype, a currency becoming another, there is ALWAYS a "rate" attached to this. So the question "$100>¥10" you asked above requires more data, it should be "$100>¥10 @ 144.28". ANYTHING else is a terrible leaky abstraction. Don't do it. Source your rates automatically from a single source if you like, but make it explicit.
Anyway, a "Money" object really is just this: A precise decimal object, with an ISO currency code. The latter simply being a short string among an included, limited set.
Money is never converted. It is exchanged. Trying to solve this is like trying to solve the question "Is "100 USD" > "1 LAPTOP".
When you turn 100 USD into 90 EUR, you didn't convert it. You exchanged it. You bought EUR, at a price given to you by someone or something exchanging it. This could be a bank, a well-established currency office, or some dude on the street. There is no real difference between all three of those: The third party gave you a price, and now has more USD and less EUR, whereas you have more EUR and less USD.
There are various entities publishing standardized average rates which are calculated after the day closes, based on a variety of datapoints they have access to. Those are often used in eg. accounting, to establish the "real" value of something you bought in a currency you don't often use, but it's not true conversion.
If you have, as a datatype, a currency becoming another, there is ALWAYS a "rate" attached to this. So the question "$100>¥10" you asked above requires more data, it should be "$100>¥10 @ 144.28". ANYTHING else is a terrible leaky abstraction. Don't do it. Source your rates automatically from a single source if you like, but make it explicit.
Anyway, a "Money" object really is just this: A precise decimal object, with an ISO currency code. The latter simply being a short string among an included, limited set.