New in .NET 10.0 [7]: Semi-Auto Properties in C# 14.0

In the document “What’s new in C# 14,” Microsoft describes the keyword field, which can be used to create so-called semi-auto properties.

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However, this language feature already exists in the stable version of .NET 9.0 – but in the “Preview” status. This means that you had to set <LangVersion>preview</LangVersion> for it. The mention in “What’s new in C# 14” suggests that the language feature will finally be considered stable in C# 14.0.

The following code shows a semi-auto property with the keyword field, which automatically creates a field for the property:

 /// <summary>
 /// Semi-Auto Property
 /// </summary>
 public int ID
 {
  get;
  set // init wäre hier auch erlaubt!
  {
   if (value < 0) throw new ArgumentOutOfRangeException();
   if (field > 0) throw new ApplicationException("ID schon gesetzt");
   field = value;
  }
 } = -1;

If there is already a data member named field in (older) program code, the compiler will warn that it is no longer being used. This may represent a breaking change, for example, if serialization exists for the data member field. However, developers can force the use of the old data member by writing @field or this.field in the program code.

(kbe)