Arithmetic Operations

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

Whilst money does support a number of arithmetic operations that take a double as the operator this is STRONGLY DISCOURAGE. Doubles are imprecise and will introduce rounding errors.

Where ever possible used the methods that take a Fixed, Int or BigInt.

MultiplyByFixed

Multiply a Money instance by a Fixed instance.

final kr = Currency.create('KR', 0);
final amount = Money.parseWithCurrency('100', kr, pattern: 'S0');
final halfish = amount.multiplyByFixed(Fixed.parse('0.4', ));
expect(halfish, equals(Money.fromIntWithCurrency(40, kr)));
expect(halfish.decimalDigits, equals(0));

Multiply by num (double or int)

The '*' operator takes a num and converts it to a Fixed value with 16 decimal places. However the scale of the result is dictated by the Money instance passed to the '*' operator.

/// Create the KR currency with 0 decimal digits.
final kr = Currency.create('KR', 0);
/// parse '100' to get a Money storing KR100.
final amount = Money.parseWithCurrency('100', kr, pattern: 'S0');
/// Multiply by 0.4 to get KR40
final halfish = amount * 0.4;
expect(halfish, equals(Money.fromIntWithCurrency(40, kr)));
/// scale of the results is 0 as dictated by the Currency.
expect(halfish.decimalDigits, equals(0));

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';
    test('Operators', () {
      final fiveDollars = Money.parse('5.00', isoCode: 'USD');
      final tenDollars = fiveDollars + fiveDollars;
      expect(tenDollars.minorUnits.toInt(), equals(1000));
      final zeroDollars = fiveDollars - fiveDollars;
      expect(zeroDollars.minorUnits.toInt(), equals(0));

      final fifteenCents = Money.fromBigInt(BigInt.from(15), isoCode: 'USD');

      final thirtyCents = fifteenCents * 2; // $0.30
      expect(thirtyCents.minorUnits.toInt(), equals(30));
      final eightCents = fifteenCents * 0.5; // $0.08 (rounded from 0.075)
      expect(eightCents.minorUnits.toInt(), equals(8));
    });