github.com/unwittingabse/money

money

Package money implements immutable monetary amounts and exchange rates for Go.

Key Features

• Immutability - Once set, an amount or exchange rate remains constant, ensuring safe concurrent access across goroutines.
• Banker's Rounding - Uses half-to-even rounding, also known as "banker's rounding", to minimize cumulative rounding errors commonly seen in financial calculations.
• No Panics - All methods are panic-free, returning errors instead of crashing your application in cases such as overflow, division by zero, or currency mismatch.
• Zero Heap Allocation - Optimized to avoid heap allocations, reducing garbage collector impact during arithmetic operations.
• High Precision - Supports up to 19 digits of precision, representing amounts from -99,999,999,999,999,999.99 to 99,999,999,999,999,999.99 inclusive.
• Correctness - Arithmetic operations are cross-validated against the cockroachdb/apd and shopspring/decimal packages through extensive fuzz testing.

Getting Started

Installation

To add the money package to your Go workspace:

go get github.com/unwittingabse/money

Basic Usage

Create an amount using one of the constructors. After creating an amount, you can perform various operations as shown below:

package main

import (
    "fmt"
    "github.com/govalues/decimal"
    "github.com/unwittingabse/money"
)

func main() {
    // Constructors
    a, _ := money.NewAmount("USD", 8, 0)               // a = $8.00
    b, _ := money.ParseAmount("USD", "12.5")           // b = $12.50
    c, _ := money.NewAmountFromFloat64("USD", 2.567)   // c = $2.567
    d, _ := money.NewAmountFromInt64("USD", 7, 896, 3) // d = $7.896
    r, _ := money.NewExchRate("USD", "EUR", 9, 1)      // r = $/€ 0.9
    x, _ := decimal.New(2, 0)                          // x = 2

    // Operations
    fmt.Println(a.Add(b))          // $8.00 + $12.50
    fmt.Println(a.Sub(b))          // $8.00 - $12.50
    fmt.Println(a.SubAbs(b))       // abs($8.00 - $12.50)

    fmt.Println(a.Mul(x))          // $8.00 * 2
    fmt.Println(a.AddMul(b, x))    // $8.00 + $12.50 * 2
    fmt.Println(a.SubMul(b, x))    // $8.00 - $12.50 * 2
    fmt.Println(r.Conv(a))         // $8.00 * $/€ 0.9

    fmt.Println(a.Quo(x))          // $8.00 / 2
    fmt.Println(a.AddQuo(b, x))    // $8.00 + $12.50 / 2
    fmt.Println(a.SubQuo(b, x))    // $8.00 - $12.50 / 2
    fmt.Println(a.QuoRem(x))       // $8.00 div 2, $8.00 mod 2
    fmt.Println(a.Rat(b))          // $8.00 / $12.50
    fmt.Println(a.Split(3))        // $8.00 into 3 parts

    // Rounding to 2 decimal places
    fmt.Println(c.RoundToCurr())   // 2.57
    fmt.Println(c.CeilToCurr())    // 2.57
    fmt.Println(c.FloorToCurr())   // 2.56
    fmt.Println(c.TruncToCurr())   // 2.56

    // Conversions
    fmt.Println(d.Int64(9))        // 7 896000000
    fmt.Println(d.Float64())       // 7.896
    fmt.Println(d.String())        // USD 7.896

    // Formatting
    fmt.Printf("%v", d)            // USD 7.896
    fmt.Printf("%[1]f %[1]c", d)   // 7.896 USD
    fmt.Printf("%f", d)            // 7.896
    fmt.Printf("%c", d)            // USD
    fmt.Printf("%d", d)            // 790
}

Documentation

For detailed documentation and additional examples, visit the package documentation.

Comparison

Comparison with other popular packages:

Feature	govalues	rhymond v1.0.10	bojanz v1.2.1
Speed	High	Medium	Medium
Numeric Representation	Floating Point	Fixed Point	Floating Point
Precision	19 digits	18 digits	39 digits
Default Rounding	Half to even	Not supported	Half up
Overflow Control	Yes	No1	Yes
Support for Division	Yes	No	Yes
Support for Currency Conversion	Yes	No	Yes

Benchmarks

goos: linux
goarch: amd64
pkg: github.com/unwittingabse/money-tests
cpu: AMD Ryzen 7 3700C  with Radeon Vega Mobile Gfx 

Test Case	Expression	govalues	rhymond v1.0.10	bojanz v1.2.1	govalues vs rhymond	govalues vs bojanz
Add	$2.00 + $3.00	22.95n	218.30n	144.10n	+851.41%	+528.02%
Mul	$2.00 * 3	21.80n	133.40n	239.60n	+511.79%	+998.83%
Quo (exact)	$2.00 / 4	80.12n	n/a	468.05n	n/a	+484.19%
Quo (inexact)	$2.00 / 3	602.1n	n/a	512.4n	n/a	-14.91%
Split	$2.00 into 10 parts	374.9n	897.0n	n/a	+139.28%	n/a
Conv	$2.00 to €	30.88n	n/a	348.50n	n/a	+1028.38%
Parse	$1	44.99n	139.50n	99.09n	+210.07%	+120.26%
Parse	$123.456	61.45n	148.60n	240.90n	+141.82%	+292.03%
Parse	$123456789.1234567890	131.2n	204.4n	253.0n	+55.85%	+92.87%
String	$1	38.48n	200.70n	89.92n	+421.50%	+133.65%
String	$123.456	56.34n	229.90n	127.05n	+308.02%	+125.49%
String	$123456789.1234567890	84.73n	383.30n	277.55n	+352.38%	+227.57%
Telco	see specification	224.2n	n/a	1944.0n	n/a	+766.89%

The benchmark results shown in the table are provided for informational purposes only and may vary depending on your specific use case.

Footnotes

• rhymond does not detect overflow and returns an invalid result. For example, 92,233,720,368,547,758.07 + 0.01 results in -92,233,720,368,547,758.08. ↩