[ANN] ExchangeRates.jl

Package Announcements
1

I often need to convert prices in webshops to my local currency to better understand it.
This small package ExchangeRates.jl does this with a (in my opinion) slick interface:

julia> using ExchangeRates
[ Info: Fetching rates from https://www.ecb.europa.eu/stats/eurofxref/eurofxref-daily.xml

julia> 100€/DKK
746.02

I hope this will also be useful for others.

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The interface appears to be a bit backwards if you consider the currencies to be units, i.e., you use €/DKK to produce a result in DKK, rather than DKK/€.

Does DKK/€ not translate to the number of Danish crowns per euro?

Edit, turns out I’m the one getting it backwards

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100EUR/DKK is the amount of DKK needed to get 100 EUR.
You can read the “/” as “in”.

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To me the easiest way to see that this interface makes sense is the following: If you multiply the equation 100 €/DKK = 746.02 by DKK, you obtain 100 € = 746.02 DKK, which makes total sense to me. Thanks for the package!

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You know that you could overload the in operator?

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Seems consistent to me: 1 m / mm = 1 m / (1 mm) = 1000. To me 100€/DKK reads as 100 Euros divided by 1 DKK, not as 100 Euros multiplied by the ratio EUR/DKK (that would be 100 €^2 / DKK).

Does DKK/€ not translate to the number of Danish crowns per euro?

No, just like mm/m is 0.001, i.e. the number of meters in a millimeter, not 1000 (the number of millimeters in a meter).

Overloading the in operator is a bad idea here – it is not the usual semantic meaning of in (set inclusion). That type of overload is frequently called “punning” and is discouraged similarly to how piracy is discouraged.

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That’s funny, I would have said exactly 1000 :wink: , but you are right.

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Neat!

I’m sure this is pretty quick, but I wonder if you’ve considered using a cached file that automatically refreshes when it’s >age old?

Disclaimer: this comes to mind because it’s one of the things that DataToolkit does (but it won’t be a good dep for other packages until the next minor release).

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I have considered that, and Scratch.jl looks like a way to do it. I’ll also look into DataToolkit.jl.
It may come in a later release, but for now I prioritized the simplicity of just fetching at load time.

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Can I use the average exchange rate in 2024?

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It is using the European Central Bank reference rates, but other sources might be possible.
I do not know a source of average exchange rates.

1 Like