The contextual keywordfield, added as a preview feature in C# 13, can be used in a property accessor to access the compiler synthesized backing field of a property. This syntax enables you to define the body of aget orset accessor and let the compiler generate the other accessor as it would in an automatically implemented property.

The addition of thefield contextual keywords provides a smooth path to add benefits such as range checking to an automatically implemented property. This practice is shown in the following example:

class TimePeriod4{    public double Hours {        get;        set => field = (value >= 0)            ? value            : throw new ArgumentOutOfRangeException(nameof(value), "The value must not be negative");    }}

You might implement theHours property as an automatically implemented property. Then, you discover that you want to protect against a negative value. You usefield and provide range checking in theset accessor. You don't need to declare the backing field by hand and provide a body for theget accessor.

For more information, see theProperties andIndexers articles.

C# language specification

For more information, see theC# Language Specification. The language specification is the definitive source for C# syntax and usage.