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Nullable-context

Handbook C# · Practical Guide

Manages nullable annotations and nullable warnings. Does not insert automatic null checks at runtime.

Simple example (Example.cs)

Save this example separately as Example.cs. Run it independently of the other examples on this page.

Example.cs:

// PROJECT-EXAMPLE
#nullable enable
string? name = null;
System.Console.WriteLine(name ?? "Unknown");

Result:

Unknown

Syntax

#nullable enable / disable / restore / enable warnings / enable annotations

Example 1

#nullable enable
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        string? name = null;
        Console.WriteLine(name ?? "Unknown");
    }
}

Example 2

#nullable enable annotations
#nullable enable warnings
using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Runtime.InteropServices;
using System.Runtime.CompilerServices;

public static class Program
{
    public static async Task Main(string[] args)
    {
        string? text = "ore";
        if (text is not null) Console.WriteLine(text.Length);
    }
}

Official source: Microsoft Learn.