EN CSharp Keyword notnull

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C#: notnull

Handbook C# · Practical Guide

Generic-restriction for a type that must be non-nullable. Violations are evaluated by nullable analysis, not automatic runtime exclusion.

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
T Echo<T>(T value) where T : notnull => value;
System.Console.WriteLine(Echo("ore"));

Result:

ore

Syntax

where T : notnull

Example 1: simple form

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)
    {
        Console.WriteLine(Values.Identity("ore"));
    }
}
public static class Values { public static T Identity<T>(T value) where T : notnull => value; }

Example 2: another practical form

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)
    {
        Storage<int> storage = new();
        storage.Put(1, "ore");
        Console.WriteLine(storage.Get(1));
    }
}
public class Storage<TKey> where TKey : notnull { private readonly Dictionary<TKey, string> values = new(); public void Put(TKey key, string value) { values[key] = value; } public string Get(TKey key) => values[key]; }

Official source: Microsoft Learn.