Error: default constructor is already defined

Question

In Dart, I have the following code:

class FirstClass {
  FirstClass(a) {

  }
}

class SecondClass extends FirstClass {

}

This causes and error on SecondClass because the FirstClass does not have a default constructor.

However when I try to add one.

class FirstClass {
  FirstClass(a) {

  }

  FirstClass() {

  }
}

It errors because the default constructor is already defined in FirstClass.

The only way I can seem to make this work and not error is if the superclass does not implement any constructors at all. What am I doing wrong?

Answer 1

In dart you can not have the same method/constructor name used several times (even with different parameters).

In your case you can either use named constructor to define 2 constructors :

class FirstClass {
  FirstClass() {}
  FirstClass.withA(a) {}
}

or define a as optional and keep only one constructor :

class FirstClass {
  FirstClass([a]) {}
}