Why does C# not warning about non-nullable long field?-CodePudding

Why do I not get a non-nullable warning (or some other warning) for FieldTwo not being set in the constructor? I'm using .Net 5.0 and Nullable option is set to true in the project file.

  public class MyClass
  {
    public string FieldOne;
    public long FieldTwo;

    public MyClass (string p1, long p2)
    {
      FieldOne = p1;
      // FieldTwo is not set. Where is the non-nullable warning!?
    }
  }

CodePudding user response：

long is a value type and cannot be null. So there is no reason for warn about null. What I suspect you want is a field not initialized warning.

If a private field is never assigned, it causes a CS0649 warning. However, if the field public, or is modified anywhere in the class, this warning is not raised. For example, the following would be perfectly acceptable code, and should not give a warning:

public class MyClass{
    private long myLong;
    public void Increment() => myLong  ;
}

If the field should only be set from the constructor you should declare it as readonly. However, public readonly fields does not trigger a warning, even if they probably should. See Why do I NOT get warnings about uninitialized readonly fields?.

CodePudding user response：

long is a value type and can't be null. Value types are always initialized when declared with a default value, in this case 0. You'd have to change the field type to long? if you wanted to store a null

Those fields aren't properties anyway. This isn't just semantics. Fields are implementation details, even public fields. They aren't considered part of a class's API surface. Properties are part of the API, they get serialized by default by all serializers (fields don't) and guarantee In fact having public fields is a code smell.

To ensure all properties are initialized you can use a record type instead of a class :

public record(string PropertyOne, long PropertyTwo);

This generates a class with init-only properties for PropertyOne and PropertyTwo and a constructor that requires values for all properties. Along with equality operators, deconstructors and a ToString() implementation that returns all properties in the form of a JSON string.