Arithmetic Operations

The Money class is immutable, so each operation returns a new Money instance.

Money uses fixed scale (no. of decimals) mathemtatics operations which can lead to some expected results.

import 'money2.dart';
/// 0 decimal place currency.
final Currency kr = Currency.create('KR', 0);
final Money amount = Money.parse(r'100', kr, 'S0');
final halfish = amount * 0.4;
print(halfish);
0

The problem with the above equation is that `amount` has a scale of 0. As we don't know the scale of the double (0.4) we use the scale of the amount. The resuls in 0.4 being rounded down to zero.

The correct way to handle this is to first convert the double to a Fixed instance with the desired scale.

import 'money2.dart';
/// 0 decimal place currency.
final Currency kr = Currency.create('KR', 0);
final Money amount = Money.parse(r'100', kr, 'S0');
final halfish = amount * Fixed.fromNum(0.4, scale: 1);
print(halfish);
40

Money provides the following arithmetic operators:

• unary -()

• +(Money)

• -(Money)

• *(num)

• /(num)

Operators + and - must be used with operands in same currency, otherwise ArgumentError will be thrown.

import 'package:money2/money2.dart';
final tenDollars = fiveDollars + fiveDollars;
final zeroDollars = fiveDollars - fiveDollars;

Operators *, / receive a num as the second operand. Both operators use schoolbook rounding to round result up to a minorUnits of a currency.

import 'package:money2/money2.dart';
final fifteenCents = Money.fromBigInt(BigInt.from(15), code: 'USD');

final thirtyCents = fifteenCents * 2;  // $0.30
final eightCents = fifteenCents * 0.5; // $0.08 (rounded from 0.075)