What are Ref locals and Ref returns in C# 7.0?

A reference return value allows a method to return a reference to a variable, rather than a value.

The caller can then choose to treat the returned variable as if it were returned by value or by reference.

The caller can create a new variable that is itself a reference to the returned value, called a ref local.

In the below example even though we modify the color it doesn't have any mpact on the original array colors

Example

class Program{
   public static void Main(){
      var colors = new[] { "blue", "green", "yellow", "orange", "pink" };
      string color = colors[3];
      color = "Magenta";
      System.Console.WriteLine(String.Join(" ", colors));
      Console.ReadLine();
   }
}

Output

blue green yellow orange pink

To acheive this we can make use of ref locals

Example

public static void Main(){
   var colors = new[] { "blue", "green", "yellow", "orange", "pink" };
   ref string color = ref colors[3];
   color = "Magenta";
   System.Console.WriteLine(String.Join(" ", colors));
   Console.ReadLine();
}

Output

blue green yellow Magenta pink

Ref returns −

In the below example even though we modify the color it doesn't have any mpact on the original array colors

Example

class Program{
   public static void Main(){
      var colors = new[] { "blue", "green", "yellow", "orange", "pink" };
      string color = GetColor(colors, 3);
      color = "Magenta";
      System.Console.WriteLine(String.Join(" ", colors));
      Console.ReadLine();
   }
   public static string GetColor(string[] col, int index){
      return col[index];
   }
}

Output

blue green yellow orange pink

Example

class Program{
   public static void Main(){
      var colors = new[] { "blue", "green", "yellow", "orange", "pink" };
      ref string color = ref GetColor(colors, 3);
      color = "Magenta";
      System.Console.WriteLine(String.Join(" ", colors));
      Console.ReadLine();
   }
   public static ref string GetColor(string[] col, int index){
      return ref col[index];
   }
}

Output

blue green yellow Magenta pink