Suppose I decorate a function like this so:

SomeType myFuntion( int x ) {
  . . .
}

Suppose, I'd like to make it polymorph and accept an int or a String as parameter x.

In this case I may declare x as dynamic. Unfortunately, the function shouldn't be that dynamic. It should not accept any typed value.

Q: May I somehow declare ( int | String ) as type alternatives?

CodePudding user response：

Unfortunately, Dart doesn't support this. However, you could use extension methods to do something similar.

With Extension Methods

extension StringX on String {
  /// Used to do something on an `int` like this:
  ///
  /// ### Example
  /// 'SomeString'.myFunction()
  ///
  String myFunction() {
    // directly call any function you would normally call on a string
    // Below is the same as calling `this.substring...`
    return substring(0, 1).toUpperCase()   substring(1);
  }
}

extension IntX on int {
  /// Used to do something on an `int` like this:
  ///
  /// ### Example
  /// 42.myFunction()
  ///
  SomeType myFunction() {
    return this *
        4; // `this` is a reference to the int this method was called on
  }
}

CodePudding user response：

You could also use Functional Programming with the help of the Dartz package.

import 'package:dartz/dartz.dart';

Either<int, String> doSomething(bool flag) {
  return flag ? Left(123) : Right("One Two Three");
}

void main() {
  final flags = [true, false];
  flags.map((flag) => doSomething(flag).fold(
      (myNum) => print('Got the number $myNum'),
      (myStr) => print('Got the string "$myStr"')));
}

Added benefit of this solution: you know which type (Left or Right) you get back from your function.