sandbox currency and Money types

Messy experiment playing with types and interfaces, and experiment with currency (Money) types

Creating currency objects

zar1 := money.NewZAR(18325.01)
zar2 := money.NewZAR(18325.99)
gbp1 := money.NewGBP(50.95))

Comparing

.Greater(), .GreaterThan(), .Equal(), .LessThan() etc

if zar1.Greater(zar2) {
    ...
}

Printing

fmt.Println("|", gbp1.Wide(), "|")
fmt.Println("|", gbp1.Narrow(), "|")

produces

Standard 14 and 7 digit wide columnformats respectively.

| £          50.95 |
| £   50.95 |

Cloning with new Value

Clone the currency type and formatting;

gbp2:= gbp1.Clone(123.45)

type safety

You can't add or substract different currency types. Compiler will prevent that.

Small account service created using the currency types

Example code can be run as follows

func TestAccountService() {
	as := accountservice.New("accounts.json")
	as.CreateAccount("H1", "Harrys account", money.NewGBP(0.01))
	as.CreateAccount("H2", "Haggard account", money.NewGBP(4500))
	as.CreateAccount("N1", "Nelly account1", money.NewZAR(18325.01))
	as.CreateAccount("N2", "Nelly account2", money.NewZAR(18325.99))
	as.CreateAccount("C1", "Chandler account", money.NewGBP(50.95))
	as.Dump()
	fmt.Println("---")
	as.Transfer("H2", "H1", money.NewGBP(0.01))
	as.Dump()
}

Produces the following output

Adding additional currencies

In order to get type safety (without code generation or generics) you need to implement (add) 1 new file per additional currency and implement the following reciever methods. _ example below is from gbp.go _

package money

import "fmt"

// GBP money
type GBP struct{ Money }

// NewGBP returns a NewGBP money
func NewGBP(amount float64) GBP {
	m := new2DecimalFormatLeft("£", amount)
	return GBP{m}
}

// Add ...
func (m GBP) Add(rhs GBP) Money {
	return m.Clone(m.allDigits + rhs.allDigits)
}

// Subtract ...
func (m GBP) Subtract(rhs GBP) GBP {
	return GBP{m.Money.Clone(m.allDigits - rhs.allDigits)}
}

// GreaterOrEqual ...
func (m GBP) GreaterOrEqual(rhs GBP) bool {
	return m.allDigits >= rhs.allDigits
}

// Greater ...
func (m GBP) Greater(rhs GBP) bool {
	return m.allDigits > rhs.allDigits
}

// Equal ...
func (m GBP) Equal(rhs GBP) bool {
	return m.allDigits == rhs.allDigits
}

// LessThan ...
func (m GBP) LessThan(rhs GBP) bool {
	return m.allDigits < rhs.allDigits
}

// GetMoney ...
func (m GBP) GetMoney() Money {
	return m.Money
}

// Wide ...
func (m GBP) Wide() string {
	return fmt.Sprintf(m.formatWide, m.integralDigits, m.fractionalDigits)
}

// Short ...
func (m GBP) Short() string {
	return fmt.Sprintf(m.formatShort, m.integralDigits, m.fractionalDigits)
}

useful links

https://floating-point-gui.de/formats/integer/ : see the note and warning NOT to use integers if at all possible.
https://floating-point-gui.de/xkcd/

goblinfactory / go-playground-currency