return - Returning two lists in C#

Question

I have been researching this for a while now, and am still unsure on how to implement and what is the best way to return two lists from a separate method?

I know there are similar question floating around but they seem to contradict each other as to which is the best way to do this. I just need simple and effective resolution to my problem. Thanks in advance.

Answer 1

There are many ways.

1. Return a collection of the lists. This isn't a nice way of doing it unless you don't know the amount of lists or if it is more than 2-3 lists.

   public static IEnumerable<List<int>> Method2(int[] array, int number)
   {
       return new List<List<int>> { list1, list2 };
   }
   

2. Create an object with properties for the list and return it:

   public class YourType
   {
       public List<int> Prop1 { get; set; }
       public List<int> Prop2 { get; set; }
   }
   
   public static YourType Method2(int[] array, int number)
   {
       return new YourType { Prop1 = list1, Prop2 = list2 };
   }
   

3. Return a tuple of two lists - Especially convenient if working with C# 7.0 tuples

   public static (List<int>list1, List<int> list2) Method2(int[] array, int number) 
   {
       return (new List<int>(), new List<int>());
   }
   
   var (l1, l2) = Method2(arr,num);
   

   Tuples prior to C# 7.0:

   public static Tuple<List<int>, List<int>> Method2(int[] array, int number)
   {
       return Tuple.Create(list1, list2); 
   }
   //usage
   var tuple = Method2(arr,num);
   var firstList = tuple.Item1;
   var secondList = tuple.Item2;
   

I'd go for options 2 or 3 depending on the coding style and where this code fits in the bigger scope. Before C# 7.0 I'd probably recommend on option 2.