C# 14.0: Introducing the field keyword

In this post, let's have a look at a nice feature that is coming with C# 14.0. 

Currently it's still on preview, so you can try this feature out with .NET 9.0 (C# 14.0 is supported on .NET 10 though) or .NET 10 .0 with LangVersion set to preview.

<PropertyGroup>
  <TargetFramework>net9.0</TargetFramework>
  <LangVersion>preview</LangVersion>
  ...
</PropertyGroup>

or

<PropertyGroup>
  <TargetFramework>net10.0</TargetFramework>
  <LangVersion>preview</LangVersion>
  ...
</PropertyGroup>

Now let's have a look.

Consider the following class.

public class Employee
{
    // Other properties
 
    public required DateOnly Birthday { get; set; }
}

Say you have a requirement, where Employees Age needs to be >= 21. We can introduce that validation when setting a value for the Birthday, but in order to do that, and just for that, we need to add a backing field for Birthday, something like below:

public class Employee
{
    private const int MinAge = 21;
 
    // Other properties
 
    private DateOnly _birthday;
 
    public required DateOnly Birthday
    {
        get => _birthday;
        set
        {
            ArgumentOutOfRangeException.ThrowIfLessThan(value, 
                DateOnly.FromDateTime(DateTime.Now.AddYears(-MinAge)));
 
            _birthday = value;
        }
    }
}

But what if we can do the same without using the backing field? C# 14.0 introduces a new contextual keyword field.

public class Employee
{
    private const int MinAge = 21;
 
    // Other properties
 
    public required DateOnly Birthday
    {
        get;
        set
        {
            ArgumentOutOfRangeException.ThrowIfLessThan(value, 
                DateOnly.FromDateTime(DateTime.Now.AddYears(-MinAge)));
 
            field = value;
        }
    }
}

So here just as a value contextual keyword, we now have a field contextual keyword. We no longer need the backing field, therefore we also don't need to provide a body for the get accessor.

I am loving it.

Keep watching this space for more C# 14.0 features:
   What's new in C# 14

Happy Coding.

Regards,

Jaliya