call_objects.dart

/*
 * Dart & Flutter - Training
 * 
 * Copyright (c) Boris-Wilfried Nyasse
 * All rights reserved
 * 
*/

// Define a class 'Adder' that behaves like a function.
class Adder {
  // 'initial' is a final integer that will be added to the sum of the list.
  final int initial;

  // Constructor takes an initial value.
  Adder(this.initial);

  // Overriding the 'call' method to make this object callable.
  // It takes a list of integers and returns their sum added to 'initial'.
  int call(List<int> values) => values.fold(
        initial,
        (a, b) => a + b,
      );
}

// Function that takes another function as a parameter.
// The function parameter takes a list of integers and returns an integer.
void takesFun(int Function(List<int>) fun) {
  print("Fun: ${fun([50])}");
}

void main() {
  // Create an instance of 'Adder' with an initial value of 10.
  final add10 = Adder(10);

  // The instance 'add10' can be called as if it's a function.
  // This prints the sum of 20 and the initial value 10.
  print(add10([20])); // 30

  // Calling 'add10' with a list of values. It adds all values in the list to the initial value.
  print(add10([20, 30, 40])); // 100

  // 'takesFun' takes a callable object. Here 'add10' is passed and executed within 'takesFun'.
  takesFun(add10); // 60
}