Fraction.fromString constructor

Fraction.fromString(String value)

Returns an instance of Fraction if value represents a valid fraction. Some correct examples are:

 Fraction.fromString("5/2")
 Fraction.fromString("-5/2")
 Fraction.fromString("5")

The denominator cannot be negative or zero:

 Fraction.fromString("5/-2") // throws
 Fraction.fromString("5/0") // throws

If the given value doesn't represent a fraction, a FractionException object is thrown.

Implementation

factory Fraction.fromString(String value) {
  // Check the format of the string
  if ((!_fractionRegex.hasMatch(value)) || (value.contains('/-'))) {
    throw FractionException('The string $value is not a valid fraction');
  }

  // Remove the leading + (if any)
  final fraction = value.replaceAll('+', '');

  // Look for the '/' separator
  final barPos = fraction.indexOf('/');

  if (barPos == -1) {
    return Fraction(int.parse(fraction));
  } else {
    final den = int.parse(fraction.substring(barPos + 1));

    if (den == 0) {
      throw const FractionException('Denominator cannot be zero');
    }

    // Fixing the sign of numerator and denominator
    return Fraction(int.parse(fraction.substring(0, barPos)), den);
  }
}