monies

Ruby gem for representing monetary values.

Pure Ruby—compatible with MRI/CRuby, JRuby, TruffleRuby, and Natalie.

Installation

Using Bundler:

$ bundle add monies

Using RubyGems:

$ gem install monies

Usage

Getting started:

require 'monies'

a = Monies(11, 'USD')
b = Monies('22.22', 'USD') * 2
c = Monies.parse('$33.44')

puts Monies.format(a + b + c, symbol: true)

Currencies

Currencies are represented as strings. Using ISO 4217 currency codes is recommended for maximum interoperability, however there are no restrictions on what strings you can use. For example:

Monies(10, 'USD')
Monies(10, 'BTC')
Monies(10, 'GBX')
Monies(10, 'X')
Monies(10, 'LOL')
Monies(10, 'Cubit')
Monies(10, 'Latinum')
Monies(10, 'sats')

If your application primarily uses a single currency you can set a default currency:

Monies.currency = 'USD'

Monies(10)

Arithmetic

Arithmetic is currency checked to prevent errors:

Monies(1, 'USD') + Monies(1, 'RUB')  # raises Monies::CurrencyError

If you need to sum amounts in different currencies you should first convert them all to the same currency.

Division is limited to 16 decimal places by default, which ought to be enough for everyone. If you need more accuracy you can use the #div method to specify the maximum number of decimal places you want:

Monies(1, 'USD').div(9, 100)

Use the #allocate method to split an amount into a number of smaller amounts:

installments = Monies(1, 'USD').allocate(3, 2)

Currency conversion

Use the #convert method to convert instances to another currency:

value = Monies('1.23', 'BTC')

price = Monies(100_000, 'USD')

puts value.convert(price).round(2)

Fetching price data, caching that data, and rounding the result are all responsibilities of the caller.

Parsing strings

Use the Monies method to convert strings that are expected to be valid and don't contain special formatting, such as those in source code and databases:

Monies('12345.6')

Use the Monies.parse method to parse strings that could be invalid or could contain special formatting like thousand separators, currency codes, or symbols:

Monies.parse('£1,999.99')
Monies.parse('1.999,00 EUR')

An ArgumentError exception is raised for invalid input:

Monies.parse('notmoney')  # raises ArgumentError

Currency symbols and currency codes are defined in Monies.symbols which can be updated to support additional currencies using #[]= or #update. For example:

Monies.symbols["\u20BF"] = 'BTC'

Monies.symbols.update({"\u20BF" => 'BTC'})

Monies.parse('1,000 BTC')

Formatting strings

Use the Monies.format method to produce formatted strings:

Monies.format(Monies('1234.56', 'USD'))  # "1,234.56"

Specify the code or symbol options to include the currency code or symbol:

Monies.format(Monies('1234.56', 'USD'), code: true)  # "1,234.56 USD"

Monies.format(Monies('1234.56', 'USD'), symbol: true)  # "$1,234.56"

Specify the name of the format to use different formatting rules:

Monies.format(Monies('1234.56', 'USD'), :eu)  # "1.234,56"

The default format is :en and can be changed by updating Monies.formats, for example to change the default format to the built-in :eu format:

Monies.formats[:default] = Monies.formats[:eu]

To create a custom format first create a Monies::Format subclass, and then add the format to Monies.formats. For example:

class CustomFormat < Monies::Format::EN
  # ...
end

Monies.formats[:custom] = CustomFormat.new

BigDecimal integration

Monies integrates with the bigdecimal gem for multiplication and currency conversion. For example:

require 'bigdecimal/util'

Monies('1.23', 'USD') * BigDecimal('0.1')

Use the Monies method to convert from a BigDecimal value:

Monies(BigDecimal(10), 'USD')

Use the #to_d method to convert to a BigDecimal value:

monies.to_d

Specify a currency argument to use BigDecimal values for currency conversion:

monies = Monies('1.11', 'BTC')
monies.convert(BigDecimal(100_000), 'USD').round(2)

Percentage integration

Monies integrates with the percentage gem for percentage calculations. For example:

require 'percentage'

capital_gains = Monies(10_000, 'GBP')

tax_rate = Percentage.new(20)

tax_liability = capital_gains * tax_rate

puts tax_liability

Sequel integration

Monies integrates with the sequel gem to support database serialization. For example:

class Product < Sequel::Model
  plugin Monies::Serialization::Sequel

  serialize_monies :price
end

This will serialize the value and the currency as a single string.

You can also specify the currency at the model/application level using the currency keyword argument:

serialize_monies :price, currency: Monies.currency

This will serialize just the value as a single string.

You can also use two columns, one for the value and an additional string column to store the currency:

serialize_monies :price, currency: :currency

ActiveRecord integration

Monies integrates with the activerecord gem to support database serialization. For example:

class Product < ApplicationRecord
  include Monies::Serialization::ActiveRecord

  serialize_monies :price
end

Usage of serialize_monies is identical to the sequel integration.

License

Monies is released under the LGPL-3.0 license.