CODEWITHSUNDEEP
dartconstantsoperator-overloading
Suragch
Suragch

Reputation: 511558

Dart: In constant expressions, operands of this operator must be of type 'num'

I created a const class like so:

class MyClass {
  const MyClass(this.x, this.y);
  final double x;
  final double y;

  MyClass operator +(MyClass other) {
    return MyClass(x + other.x, y + other.y);
  }
}

Now if I try to create a new class by adding two const values:

const objectA = MyClass(1, 4);
const objectB = MyClass(3, 2);

const objectC = objectA + objectB;

I get an error:

In constant expressions, operands of this operator must be of type 'num'.

If I use final it works, though:

final objectC = objectA + objectB;

I was going to say it's because the operator overload method creates a new class at runtime, but objectA and objectB were also created at runtime and they're constants. So why can't Dart allow objectC to be const?

Upvotes: 1

Views: 429

Answers (1)

Number 3434
Number 3434

Reputation: 34

There is currently no way to define a constant operator that accepts and returns classes other than num in Dart.

You cannot use these operators as constant expressions, unless it only accepts and returns the type num. Dart cannot ensure that the expression is actually constant.

To be more precise, what this error actually means is "The operator you are calling is not constant."

Upvotes: 0

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