Switching On Types in C# & .NET

In our previous post, “Using Declaration Patterns in C# & .NET”, we looked at how to simplify polymorphic code using the declaration pattern.

In today’s post, we will look at another solution: switching against types.

The type hierarchy is as follows:

public abstract record Animal(string Name, int Legs);
public record Primate(string Name, int Legs) : Animal(Name, Legs);
public record Bird(string Name, int Legs, byte Wings) : Animal(Name, Legs);

Then suppose we have a collection like this:

Animal[] animals =
[
  new Primate("Baboon", 4),
  new Primate("Chimpanzee", 4),
  new Bird("Chicken", 2, 2),
  new Bird("Turkey", 2, 2),
];

If we needed to selectively process each Animal, we could do it like this:

void Process(Animal animal)
{
  switch (animal)
  {
    case Primate primate:
      Console.WriteLine($"Hello {primate.Name} Primate: you have {primate.Legs} legs");
      break;
    case Bird bird:
      Console.WriteLine($"Hello {bird.Name} bird: you have {bird.Legs} legs, {bird.Wings}");
      break;
    default:
    	Console.WriteLine("Unknown");
    break;
  }
}

The magic is taking place here:

case Primate primate:
  Console.WriteLine($"Hello {primate.Name} Primate: you have {primate.Legs} legs");
  break;

In the matching, we immediately capture the match for Primate into a correctly typed variable, primate.

Very neat.

TLDR

You can switch directly on types and capture the resulting concrete type.

The code is in my GitHub.

Happy hacking!