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Flutter – Overload the double operator in Dart

In Dart, I can override the toString method to change the string content returned by an object when it is used as a string.

I need to change the object’s behavior when it is used as a double.

I would like to achieve the same result from this C++ code in Dart:

class Value {
private:
  double value;
  Color color;

public:
  Value(double value, Color color) : value(value), color(color) {}
  operator double() const {
    return value;
  }
};

Meaning that I would be able to use an object from the class Value like this:

Value value = const Value(value: 13.0, color: Colors.blue);

double a = value + 3; // a = 16.0
double b = value - 3; // b = 10.0
double c = value; // c = 13.0
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2

Answers


  1. 0

    To achieve a similar result, you could define the addition operator + and the subtraction - operator of the Value class:

    class Value {
  final double value;
  final Color color;

  const Value({required this.value, required this.color});

  @override
  String toString() => "The value is $value.";

  double toDouble() => value;

  double operator +(num other) {
    return value + other;
  }

  double operator -(num other) {
    return value - other;
  }
}

    Your main.dart would then become:

    void main() {
  final value = Value(value: 13.0, color: Colors.blue);
  double a = value + 3; // a = 16.0
  double b = value - 3; // b = 10.0
  double c = value.toDouble(); // c = 13.0
  double d = value.value; // d = 13.0
}
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  2. 0

    you can get similar functionality by defining methods in your class to perform these operations.

    class Value {
  final double value;
  final Color color;

  Value({required this.value, required this.color});

  double add(double operand) => this.value + operand;
  double subtract(double operand) => this.value - operand;
  double toDouble() => this.value;
}

void main() {
  Value value = Value(value: 13.0, color: Colors.blue);

  double a = value.add(3); // a = 16.0
  double b = value.subtract(3); // b = 10.0
  double c = value.toDouble(); // c = 13.0
}
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