twmbx / go-money

Go implementation of Fowler's Money pattern

Money

GoMoney provides ability to work with monetary value using a currency's smallest unit. Package allows you to use basic Money operations like rounding, splitting or allocating without losing a penny. You shouldn't use float for monetary values, since they always carry small rounding differences.

package main

import "github.com/rhymond/go-money"

func main() {
	pound := money.New(100, "GBP")
	twoPounds := pound.Add(pound)

	parties, _ := twoPounds.Split(3)
	parties[0].Display() // £0.67
	parties[1].Display() // £0.67
	parties[2].Display() // £0.66
}

Quick start

Get the package via

$ go get github.com/rhymond/go-money

Features

• Provides a Money struct which stores information about an Money amount value and it's currency.
• Provides a Money.Amount struct which encapsulates all information about a monetary unit.
• Represents monetary values as integers, in cents. This avoids floating point rounding errors.
• Represents currency as Money.Currency instances providing a high level of flexibility.

Usage

Instantiation

Initialise Money by using smallest unit value (e.g 100 represents 1 pound). Use ISO 4217 Currency Code to set money Currency

pound := money.New(100, "GBP")

Comparison

Go-money lets you to use base compare operations like:

• Equals
• GreaterThan
• GreaterThanOrEqual
• LessThan
• LessThanOrEqual

In order to use them currencies must be equal

pound := money.New(100, "GBP")
twoPounds := money.New(200, "GBP")
twoEuros := money.New(200, "EUR")

pound.GreaterThan(twoPounds) // false, nil
pound.LessThan(twoPounds) // true, nil
twoPounds.Equals(twoEuros) // false, error: Currencies don't match

Asserts

• IsZero
• IsNegative
• IsPositive

Zero value

To assert if Money value is equal zero use IsZero()

pound := money.New(100, "GBP")
result := pound.IsZero(pound) // false

Positive value

To assert if Money value is more than zero IsPositive()

pound := money.New(100, "GBP")
pound.IsPositive(pound) // true

Negative value

To assert if Money value is less than zero IsNegative()

pound := money.New(100, "GBP")
pound.IsNegative(pound) // false

Operations

• Add
• Subtract
• Divide
• Multiply
• Absolute
• Negative

In Order to use operations between Money structures Currencies must be equal

Addition

Additions can be performed using Add().

pound := money.New(100, "GBP")
twoPounds := money.New(200, "GBP")
 
result, err := pound.Add(twoPounds).Display() // £3.00, nil

Subtraction

Subtraction can be performed using Subtract().

pound := money.New(100, "GBP")
twoPounds := money.New(200, "GBP")
 
result, err := pound.Subtract(twoPounds).Display() // -£1.00, nil

Multiplication

Multiplication can be performed using Multiply().

pound := money.New(100, "GBP")
 
result, err := pound.Multiply(2).Display() // £2.00, nil

Division

Division can be performed using Divide().

pound := money.New(100, "GBP")
 
result, err := pound.Divide(2).Display() // £0.50, nil

There is possibilities to lose pennies by using division operation e.g:

money.New(100, "GBP").Divide(3).Display() // £0.33

In order to split amount without losing pennies use Split() operation.

Absolute

Return absolute value of Money structure

pound := money.New(-100, "GBP")
 
result, err := pound.Absolute().Display() // £1.00

Negative

Return negative value of Money structure

pound := money.New(100, "GBP")
 
result, err := pound.Negative().Display() // -£1.00

Allocation

• Split
• Allocate

Splitting

In order to split Money for parties without losing any penny use Split().

After division leftover pennies will be distributed round-robin amongst the parties. This means that parties listed first will likely receive more pennies than ones that are listed later

pound := money.New(100, "GBP")
parties, err := pound.Split(3)

parties[0].Display() // £0.34
parties[1].Display() // £0.33
parties[2].Display() // £0.33

Allocation

To perform allocation operation use Allocate().

It lets split money by given ratios without losing pennies and as Split operations distributes leftover pennies amongst the parties with round-robin principle.

pound := money.New(100, "GBP")
parties, err := pound.Split([]int{33, 33, 33})

parties[0].Display() // £0.34
parties[1].Display() // £0.33
parties[2].Display() // £0.33

Format

To format and return Money as string use Display().

money.New(123456789, "EUR").Display() // €1,234,567.89

Contributing

Thank you for considering contributing! Please use GitHub issues and Pull Requests for Contributing.

License

The MIT License (MIT). Please see License File for more information.