duplicate_constructor

The constructor with name '{0}' is already defined.

The unnamed constructor is already defined.

The analyzer produces this diagnostic when a class declares more than one unnamed constructor or when it declares more than one constructor with the same name.

The following code produces this diagnostic because there are two declarations for the unnamed constructor:

class C {
  C();

  C();
}

The following code produces this diagnostic because there are two declarations for the constructor named m:

class C {
  C.m();

  C.m();
}

If there are multiple unnamed constructors and all of the constructors are needed, then give all of them, or all except one of them, a name:

class C {
  C();

  C.n();
}

If there are multiple unnamed constructors and all except one of them are unneeded, then remove the constructors that aren't needed:

class C {
  C();
}

If there are multiple named constructors and all of the constructors are needed, then rename all except one of them:

class C {
  C.m();

  C.n();
}

If there are multiple named constructors and all except one of them are unneeded, then remove the constructors that aren't needed:

class C {
  C.m();
}

Unless stated otherwise, the documentation on this site reflects Dart 3.8.1. Page last updated on 2025-05-08. View source or report an issue.