experimental-money

Experimental Money

Installation

$ gem install experimental-money

Usage

Here's a simple example:

Money.configure do |config|
  config.default_currency = "EUR"
  config.conversions = {
    'USD' => 1.11,
    'Bitcoin' => 0.0047
  }
end

fifty_eur = Money.new(50, 'EUR')
fifty_eur.amount   # => 50
fifty_eur.currency # => "EUR"
fifty_eur.inspect  # => "50.00 EUR"

# Currency exchange
fifty_eur.convert_to('USD') # => 55.50 USD

# Arithmetic

twenty_dollars = Money.new(20, 'USD')
fifty_eur + twenty_dollars # => 68.02 EUR
fifty_eur - twenty_dollars # => 31.98 EUR
fifty_eur / 2              # => 25 EUR
twenty_dollars * 3         # => 60 USD

# Comparations

twenty_dollars == Money.new(20, 'USD') # => true
twenty_dollars == Money.new(30, 'USD') # => false

fifty_eur_in_usd = fifty_eur.convert_to('USD')
fifty_eur_in_usd == fifty_eur          # => true

twenty_dollars > Money.new(5, 'USD')   # => true
twenty_dollars < fifty_eur             # => true

Caveats

• We are using BigDecimals. Another option could be using Integers instead. As our desired API expects to initialize Money as Money.new(float_amount, currency) we already needed to convert the amount to BigDecimal in order to avoid Float precision errors. Integers should work way faster, though.

• Precision and rounding: When talking about money we need to know its currency precision. The normal case is having two decimal positions in order to represent cents. Other currencies use up to 8 decimal places (to represent Satoshis).

  I arbitrarily set up Bitcoin precision (8) and set a default of (2) for the remaining currencies. A pull request would be needed to add weird currencies with different precision.

  Rounding: When dividing money (or converting it to another currency -which involves a division) we end up often with a number that has to be rounded. There are many ways to round 0.006 to a two decimal places number representing USD. I hardcoded the Bankers' rounding way, but for some problems it may be suitable another method.

• Last caveat: Arithmetic doesn't always represent Money operations as we expect. If we need to divide 100USD among three people and we try to do Money.new(100, "USD")/3 to know how much each of them is receiving we'll find a surprising result: It's not possible to equally divide 100USD. With the current implementation this operation would return Money.new(33.33, "USD")

Contributing

If you want to test this gem, you may want to use a gemset to isolate the requirements. We recommend the use of tools like dep and gs, but you can use similar tools like gst or bs.

The required gems for testing and development are listed in the .gems file. If you are using dep, you can create a gemset and run dep install.

After cutest is installed you can run the tests by doing make