EN CSharp Operator Collection Expression

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Collections and spread

Handbook C# · Practical Guide

Collection expression requires a target type; spread adds elements of another sequence. Don't confuse spread with range.

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
int[] first = [1, 2];
int[] all = [.. first, 3];
System.Console.WriteLine(string.Join(",", all));

Result:

1,2,3

Syntax

int[] values = [1, ..other, 5];

Example 1

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[] middle = [2, 3];
        int[] values = [1, ..middle, 4];
        Console.WriteLine(string.Join(",", values));
    }
}

Example 2

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)
    {
        List<string> names = ["ore", "wood"];
        List<string> all = [..names, "food"];
        Console.WriteLine(all.Count);
    }
}

Official source: Microsoft Learn.