The Fixed package allows you to store and perform maths on numbers with a fixed scale (fixed no. of decimal places).
All amounts are store as integers to allow precision maths to be performed.
The Fixed package allows you to have explicit control over the no. of decimals (the scale) that are stored.
Fixed instances are immutable.
After a mathematical operation you may need to build a new Fixed object with the required scale.
For multiplication the resulting scale is the sum of the two scales e.g.
0.01 * 0.02 = 0.0002
final rate = Fixed.fromMinorUnits(75486, scale: 5); // == 0.75486
final auDollars = Fixed.fromMinorUnits(100, scale: 2); // == 1.00
final usDollarsHighScale = auDollars * rate; // ==0.7548600, scale = 7
/// reduce the scale to 2 decimal places.
final usDollars = Fixed(usDollarsHighScale, scale: 2); // == 0.75
When performing division the results scale will be the larger scale of the two operands.
final winnings = Fixed.fromMinorUnits(600000, scale: 5); // == 6.00000
final winners = Fixed.fromMinorUnits(200, scale: 2); // == 2.00
final share = winnings / winners; // == 3.00000, scale = 5
Constructors
There are multiple ways you can create a Fixed object
final t2 = Fixed.fromMinorUnits(1234, scale: 3); // == 1.234
final t3 = Fixed.fromBigInt(BigInt.from(1234), scale: 3)); // == 1.234
final t4 = Fixed(t1); // == 1.234
final t5 = Fixed.parse('1.234', scale: 3); // == 1.234
// This is the least desireable method as it can introduce
// rounding errors.
final t6 = Fixed.from(1.234, scale: 3); // == 1.234
Operators
Fixed provides mathematical operations:
final t1 = Fixed.parse('1.23'); // = 1.23
final t2 = Fixed.fromMinorUnits(100, scale: 2); // = 1.00
final t3 = t1 + t2; // == 2.23
final t4 = t2 - t1; // == 0.23
final t5 = t1 * t2; // == 1.23;
final t6 = t1 / t2; // == 1.23
final t7 = -t1; // == -1.23
Comparision
final t1 = Fixed.from(1.23);
final t2 = Fixed.fromMinorUnits(123, scale: 2);
final t3 = Fixed.fromBigInt(BigInt.from(1234), scale: 3));
expect(t1 == t2, isTrue);
expect(t1 < t3, isTrue);
expect(t1 <= t3, isTrue);
expect(t1 > t3, isFalse);
expect(t1 >= t3, isFalse);
expect(t1 != t3, isTrue);
expect(-t1, equals(Fixed.fromMinorUnits(-123, scale: 2)));
expect(t1.isPositive, isTrue);
expect(t1.isNegative, isFalse);
expect(t1.isZero, isTrue);
expect(t1.compareTo(t2) , isTrue);
Parsing
You can parse numbers from strings:
var t1 = Fixed.parse('1.234', pattern: '#.#', scale: 2);
expect(t1.minorUnits.toInt(), equals(1234));
expect(t1.scale, equals(2));
var t1 = Fixed.parse('1,000,000.234', pattern: '#,###.#', scale: 2);
expect(t1.minorUnits.toInt(), equals(1000000.23));
expect(t1.scale, equals(2));
/// for countries that use . for thousand separators
var t1 = Fixed.parse('1.000.000,234', pattern: '#.###,#', scale: 2, invertSeparators);
expect(t1.minorUnits.toInt(), equals(1000000.23));
expect(t1.scale, equals(2));
Formating
You can also format numbers to strings
var t1 = Fixed.fromMinorUnits(1234, scale: 3);
expect(t3.toString(), equals('1.234'));
expect(t3.format('00.###0'), equals('00.12340'));
expect(t3.format('00.###0', invertSeparators: true), equals('00,12340'));
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