Why does dart ask me to declare an unnecessary argument?-CodePudding

Why do I need to declare a variable of type int called "idx" if it does not serve any purpose in the generate funciton below?

Random r2 = new Random();
  var list = List<int>.generate(5, (int idx) => r2.nextInt(100));

If I do not declare it dart gives me the following error

The argument type 'int Function()' can't be assigned to the parameter type 'int Function(int)'

CodePudding user response：

The List.generate has been defined as

List.generate(int length, E generator(int index),
      {bool growable = true});

So you need to provide a function to use List.generate.

If you like to ignore it you can use _.

 List<int>.generate(5, (_) => r2.nextInt(100));

CodePudding user response：

Dart is type-safe, so it expects that the type signatures of arguments match. You can't pass a int Function() where an int Function(int) is expected.

Must it be that way? No. Since the int argument is clearly unused, the compiler conceivably could automatically transform () => r2.nextInt(100) into (_) => (() => r2.nextInt(100))(). However, doing so might hide mistakes where a wrong function is passed. Dart often favors being explicit.