Dart using variable to hold set of constructor parameters, to be used in multiple constructors?-CodePudding

is there a way to use some variable or any holder to store constructor parameters, to be able to pass them to multiple constructors without repeating the values?

I think its possible if the constructor has only positional parameters (no named parameters).

var parametersHolder={
named1: "str",
named2: "lorem",
};


// normal usage
constructorA(named1: "str", named2: "lorem");

constructorB(named2: "lorem",named1: "str" );

my question is how to do the following in dart:

constructorA(parametersHolder);

constructorB(parametersHolder);

so is that achievable ?

Thanks

CodePudding user response：

You can define a class to hold your parameters like this:

class MyClass{
  late final int myInt;
  late final String myString;
  
  MyClass.firstConstructor(MyClassParams params){
    this.myInt = params.myInt;
    this.myString = params.myString;
  }
  
  MyClass.secondConstructor(MyClassParams params){
    this.myInt = params.myInt;
    this.myString = params.myString;
  }
}


class MyClassParams{
  final int myInt;
  final String myString;
  
  const MyClassParams(this.myInt, this.myString);
}

CodePudding user response：

If you really want, you could use Function.apply with a constructor tear-off:

class Foo {
  String named1;
  String named2;
  
  Foo({required this.named1, required this.named2});
  
  @override
  String toString() => 'Foo: $named1 $named2';
}

void main() {
  var namedArguments = {
    #named1: 'str',
    #named2: 'lorem',
  };
  
  var foo = Function.apply(Foo.new, null, namedArguments) as Foo;
  print(foo); // Prints: Foo: str lorem
}

Note that doing this sacrifices compile-time type-safety.