C#•2y ago

❔ Non-nullable field 'rating' must contain a non-null value when exiting constructor

Why am i getting this warning: Non-nullable field 'rating' must contain a non-null value when exiting constructor? Before exiting the constructor Rating = aRating is executed and thus rating should be set rating to "G" or "PG" right?

c#
 internal class Book
    {
        private string title;
        private string rating;
        public Book(string aTitle, string aRating)
        {
            title = aTitle;
            Rating = aRating;
        }
        public string Rating
        {
            get { return rating; }
            set { 
                if(value == "G")
                {
                    rating = value;
                }
                else
                {
                    rating = "PG";
                }
            }
        }
    }

c#
 internal class Book
    {
        private string title;
        private string rating;
        public Book(string aTitle, string aRating)
        {
            title = aTitle;
            Rating = aRating;
        }
        public string Rating
        {
            get { return rating; }
            set { 
                if(value == "G")
                {
                    rating = value;
                }
                else
                {
                    rating = "PG";
                }
            }
        }
    }

4 Replies

vdvman1•2y ago

It can't see that setting Rating always sets rating under the hood You can add [MemberNotNull(nameof(rating))] to the setter to make the compiler happy

using System.Diagnostics.CodeAnalysis;

internal class Book
{
  private string title;
  private string rating;

  public Book(string title, string rating)
  {
    this.title = title;
    Rating = rating;
  }

  public string Rating
  {
    get => rating;

    [MemberNotNull(nameof(rating))]
    set => rating = value switch
    {
      "PG" or "G" => value,
      _ => "NR"
    };
  }
}

using System.Diagnostics.CodeAnalysis;

internal class Book
{
  private string title;
  private string rating;

  public Book(string title, string rating)
  {
    this.title = title;
    Rating = rating;
  }

  public string Rating
  {
    get => rating;

    [MemberNotNull(nameof(rating))]
    set => rating = value switch
    {
      "PG" or "G" => value,
      _ => "NR"
    };
  }
}

(I also wrote a switch with pattern matching instead of the if statement, you can use your original setter body if you don't understand or don't like how that looks)

TradingRaws4SeoulObjectStoryRawsOP•2y ago

Thank you! heartowo

I haven't seen this way of writing a switch statement but it looks very concise. TY! 🙂

Pobiega•2y ago

its a "switch expression". They are very very nice.

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ Non-nullable field 'rating' must contain a non-null value when exiting constructor