EN CSharp Keyword not

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C#: not

Handbook C# · Practical Guide

Negates a pattern. It binds more tightly than the pattern combinators and and or.

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
string? name = null;
System.Console.WriteLine(name is not null);

Result:

False

Syntax

value is not pattern

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)
    {
        int value = 15;
        Console.WriteLine(value is > 10 and < 20);
        Console.WriteLine(value is 12 or 15);
        Console.WriteLine(value is not 0);
    }
}

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)
    {
        string? text = "ore";
        Console.WriteLine(text is not null and { Length: > 1 });
        Console.WriteLine(text is "ore" or "wood");
    }
}

Official source: Microsoft Learn.