rusty-money

rusty-money handles the messy parts of dealing with money like rounding, precision, parsing and internationalization. It supports ISO-4217 currencies, common crypto currencies and lets you define your own. The main items exported by the library are Money and the iso and crypto currency sets.

Usage

A Money object is created by supplying an amount and a currency. Amounts can be specified in numeric or string types but will be stored as precise decimals internally. You can select a bundled currency or make your own. Here's a quick example of how you would make your own Currency and then create some Money with it:

use rusty_money::{Money, define_currency_set};

define_currency_set!(
  video_game {
    GIL: {
      code: "GIL",
      exponent: 2,
      locale: Locale::EnUs,
      minor_units: 100,
      name: "GIL",
      symbol: "G",
      symbol_first: true,
    }
  }
);

Money::from_major(2_000, video_game::GIL);              // 2000 GIL
Money::from_minor(200_000, video_game::GIL);            // 2000 GIL
Money::from_str("2,000.00", video_game::GIL).unwrap();  // 2000 GIL

// Currencies can be looked up by code.
let gil = video_game::find("GIL").unwrap();
Money::from_major(2_000, gil);                          // 2000 GIL

Features: Currency Sets

rusty_money provides two currency sets for convenience : iso, which implements ISO-4217 currencies and crypto which implements popular cryptocurrencies. iso is enabled by default, and you can add crypto by enabling the feature:

[dependencies]
rusty-money = { version = "0.4.1", features = ["iso", "crypto"] }

The currency sets can then be used like this:

use rusty_money::{Money, iso, crypto};

Money::from_major(2_000, iso::USD);        // 2000 U.S Dollars
Money::from_major(2_000, iso::GBP);        // 2000 British Pounds
Money::from_major(2, crypto::BTC);         // 2 Bitcoin

Money objects of the same currency can be compared:

use rusty_money::{Money, iso};
let hundred = Money::from_minor(10_000, iso::USD);
let thousand = Money::from_minor(100_000, iso::USD);

println!("{}", thousand > hundred);     // false
println!("{}", thousand.is_positive()); // true

Precision, Rounding and Math

Money objects are immutable, and operations that change amounts create a new instance of Money. Amounts are stored as 128 bit fixed-precision Decimals, and handle values as large as $2^{96}$ / $10^{28}$. Operations on Money retain the maximum possible precision. When you want less precision, you call the round function, which supports three modes:

• Half Up
• Half Down
• Half Even (default)

Money can be added, subtracted, multiplied and divided like this:

use rusty_money::{Money, Round, iso};

Money::from_minor(100, iso::USD) + Money::from_minor(100, iso::USD);  // 2 USD
Money::from_minor(100, iso::USD) - Money::from_minor(100, iso::USD);  // 0 USD
Money::from_minor(100, iso::USD) * 3;                                 // 3 USD
Money::from_minor(100, iso::USD) / 3;                                 // 0.333... USD

let usd = Money::from_str("-2000.005", iso::USD).unwrap();            // 2000.005 USD
usd.round(2, Round::HalfEven);                                        // 2000.00 USD
usd.round(2, Round::HalfUp);                                          // 2000.01 USD
usd.round(0, Round::HalfUp);                                          // 2000 USD

Formatting

Calling format! or println! on Money returns a string with a rounded amount, using separators and symbols according to the locale of the currency. If you need to customize this output, the Formatter module accepts a more detailed set of parameters.

use rusty_money::{Money, iso};
let usd = Money::from_str("-2000.009", iso::USD).unwrap();
let eur = Money::from_str("-2000.009", iso::EUR).unwrap();

println!("{}", usd);                                        // -$2,000.01
println!("{}", eur);                                        // -€2.000,01;

Exchange

The library also provides two additional types - Exchange and ExchangeRates to convert Money from one currency to another.

use rusty_money::{Money, Exchange, ExchangeRate, iso};
use rust_decimal_macros::*;

// Convert 1000 USD to EUR at a 2:1 exchange rate.
let rate = ExchangeRate::new(iso::USD, iso::EUR, dec!(0.5)).unwrap();
rate.convert(&Money::from_minor(100_000, iso::USD));                    // 500 EUR

// An Exchange can be used to store ExchangeRates for later use
let mut exchange = Exchange::new();
exchange.set_rate(&rate);
exchange.get_rate(iso::USD, iso::EUR);