C# - Required Members

August 28, 2023

language-features csharp

• Allows you to specify that a property or field of a class/struct/record must be set in an object initializer.

• public class Vehicle {
      public required string Name {get; init;}
      public required bool IsTaxed {get; init;}
  
  }
  
  var m = new Vehicle() { (1)
      Name = "Test"
  };

  1	Fails to compile unless all required properties are set in the initializer.

• Useful when you have properties that are non-optional.

• Do not need to enforce required values using the constructor.

• Much more cleaner syntax.

• You can also create an optional constructor that can set the required values.

  public class Vehicle {
      public required string Name {get; init;}
      public required bool IsTaxed {get; init;}
  
      public Vehicle () { (1)
  
      }
  
      [SetsRequiredMembers] (2)
      public Vehicle (string name) {
          Name = name;
          isTaxed = false;
      }
  }

  1	The default constructor is still available.
  2	This is a new helper ctor that sets all the properties.

• Try not to use the above pattern.

  • As it is possible to add a new required field at a later date and forget to update the constructor.

  • The code crashes at runtime with a NullReferenceException.