KeepImmutableSanity.cs

public class ImmutableXYZ {
  public ImmutableXYZ() : this("", 0, -1) {
  }
  
  private ImmutableXYZ(string abc, int def, int haha)
  {
    this.abc = abc;
    this.def = def;
    this.haha = haha;
  }

  public ImmutableXYZ WithABC(string value) {
    return new ImmutableXYZ(value, this.def, this.haha);
  }

  public ImmutableXYZ WithDEF(int value) {
    return new ImmutableXYZ(this.abc, value, this.haha);
  }

  public ImmutableXYZ WithHaha(int value) {
    return new ImmutableXYZ(this.abc, this.def, value);
  }

  public readonly string ABC;
  public readonly int DEF;
  private readonly int haha;
}