EN CSharp Keyword scoped

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C#: scoped

Handbook C# · Practical Guide

scoped limits the valid lifetime of a reference or ref-like parameter value. The compiler will not allow such a reference to be returned in a way that exceeds the set lifetime. The modifier does not make the data immutable: the scoped ref allows changing the value of the caller.

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
void Add(scoped ref int value) { value += 2; }
int count = 3;
Add(ref count);
System.Console.WriteLine(count);

Result:

5

Syntax

static int Sum(scoped ReadOnlySpan<int> values);
static void Add(scoped ref int value, int amount);

Reading data from stackalloc in the scoped parameter

using System;

internal static class Program
{
    public static void Main()
    {
        ReadOnlySpan<int> readings = stackalloc int[] { 3, 5, 7 };
        Console.WriteLine(Sum(readings));
    }
    private static int Sum(scoped ReadOnlySpan<int> values)
    {
        int total = 0;
        foreach (int value in values) total += value;
        return total;
    }
}

Result:

15

Changing a number via a scoped ref without returning a reference

using System;

internal static class Program
{
    public static void Main()
    {
        int points = 10;
        Add(ref points, 4);
        Add(ref points, 6);
        Console.WriteLine(points);
    }
    private static void Add(scoped ref int value, int amount)
    {
        value += amount;
    }
}

Result:

20

Official source: Microsoft Learn.