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Tahler / currency-rs

A library providing a way to represent currencies in Rust.
http://tahler.github.io/currency-rs/currency/index.html
MIT License
8 stars 4 forks source link

dealing with taxes #3

Closed hoodie closed 8 years ago

hoodie commented 8 years ago

Hi there, I've been working with my one fork of this lib for a while, to which I had added to possibility to multiply with f64, to deal with taxes. However, I'm not sure if this is really a good idea. Alternatively this could use something like a BigInt or BigRational from num.. I'm also not sure about the operation to turn the resulting floats back into i64, whether or not to use ceil(), floor() or just round().

If you have no strong opinion about this I would ask someone at the Rust users forum for participation.

Tahler commented 8 years ago

Hey I appreciate the feedback and work you've put in! I've actually spent the past few days working on an RSA implementation in Rust, which uses BigUints. It got me thinking about the currency library and I was just considering switching to BigInts. I'll spend some time this weekend putting that and adding some use-cases, such as applying taxes. Stay tuned and I'll let you know when I publish that!

If you have any more ideas, let me know!

Thanks again, Tyler

Tahler commented 8 years ago

I have published a new version that now uses BigInt to track the coin. It implements more traits, is more robust in the string parsing and formatting, and handles some conversion and float multiplication. I have not solved the precision problem, however. Feel free to take a look at what I've published. I think rounding is the way to go, and I am very open to ideas about how to round the BigInt during multiplication. Perhaps I'll ask for help from that forum.

hoodie commented 8 years ago

Cool thanks, I'll give it a firm check tomorrow :+1:

hoodie commented 8 years ago

Hey, sorry, didn't have time so far to check it out. I still feel about unsure about floats, especially where you multiply with f32.

I was not able to hack up a test case where this produces false results, but there are cases where long floating point numbers produce garbage.

Tahler commented 8 years ago

I've got a lot of unhappiness with this last release. Right now I'm working on porting decimal from C# over to Rust, then I plan on using that to, once again, rewrite the currency library.

hoodie commented 8 years ago

:+1: There is a decimal crate, unfortunately it does not compile on stable since it uses (now no longer) unstable features. Unfortunately the author has not reacted to my issue yet :cry:

Update: I forked it here. I think your approach using integers for storing is pretty good, only in the places where you have to multiply with decimal numbers you should restrict their types. That's a cool thing about Rust, you could implement multiplication/division solely for Decimals and leave the rest as integers.