EN CSharp Keyword is

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C#: is

Handbook C# · Practical Guide

Tests a value against a type or pattern and can bind matching parts to variables.

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
object value = 7;
if (value is int number) System.Console.WriteLine(number + 1);

Result:

8

Syntax

value is Type variable / value is 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)
    {
        object value = 12;
        if (value is int number) Console.WriteLine(number + 1);
    }
}

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)
    {
        int[] values = [1, 2, 3];
        Console.WriteLine(values is [1, .., 3]);
    }
}

Official source: Microsoft Learn.