Dart constructors are not really functions

main.dart

class Greeter {
  final String name;
  Greeter(this.name);
  Greeter.withName(this.name);
  
  static Greeter staticWithName(String name) {
    return Greeter(name);
  }
  
  void greet(String who) {
    print('${name} says: Hello ${who}!');
  }
}

void main() {
  final g = Greeter('Dartinius');
  /// It is fine to pass an instance method as a function:
  ['John', 'Mary', 'Bob', 'Alice'].forEach(g.greet);
  
  /// However, one cannot pass a constructor as function:
  //['John', 'Mary', 'Bob', 'Alice'].map(Greeter).forEach((Greeter g) => g.greet('World'));
  
  /// Neither a named constructor:
  //['John', 'Mary', 'Bob', 'Alice'].map(Greeter.withName).forEach((g) => g.greet('World'));
  
  /// Instead, a static method would work, and from the call site it looks the same as a named constructor:
  ['John', 'Mary', 'Bob', 'Alice'].map(Greeter.staticWithName).forEach((g) => g.greet('World'));
  
  /// Alternatively, one may use an anonymous function to wrap the constructor:
  ['John', 'Mary', 'Bob', 'Alice'].map((String s) => Greeter(s)).forEach((g) => g.greet('Universe'));
}