reduce example with custom items

main.dart

main(){
  List<SalesItem> salesList = List.generate(10, (int i) => SalesItem(i));
	print("salesList = $salesList");
  
// the map function takes one thing and converts it to another. You can use it to take an object,
// perform an operation and return the modified object. The function below unwraps the price so that
// I have a list of ints only. (Since you technically can't "add" [SalesItem]s.
  List<int> listOfOnlyPrices =
      salesList.map<int>((SalesItem item) => item.price).toList();
  
  // The reduce function goes down the list and adds one item to the next in each list. if you have a List of ints
  // i.e. [1, 2, 3] the reduce function, if written like it is below, would return 6. It doesn't have to 
// be a sum. You can multiply, subtract, call another function, anything you want. As long as you return
// the type that your list contains. in this case, I must return an int.
  print("listOfOnlyPrices = $listOfOnlyPrices");
  int totalSales = listOfOnlyPrices.reduce((int price1, int price2) {
    return price1 + price2;
  });
  print("totalSales = $totalSales");

}

// the List.generate() constructor creates a list based on your criteria.
// It's is a faster way to write:
// 
// List<SalesItem> salesList = [];
// for (int i = 0; i < 10; i++) {
//    salesList.add(SalesItem(i));
// }
  
  
class SalesItem {
  SalesItem(this.price);

  int price;
  toString(){
    return "price = $price";
  }
}