System.Box

Benchmarks.cs

using System;
using BenchmarkDotNet.Attributes;

[MemoryDiagnoser]
public class Benchmarks
{
    object @object;

    Box<int> box;

    [GlobalSetup]
    public void Setup()
    {
        @object = int.MaxValue;
        box = new() { Value = int.MaxValue };
    }

    [Benchmark(Description = "Boxing performed by the runtime.")]
    public object RuntimeBoxing() => int.MaxValue;

    [Benchmark(Description = "Boxing performed by the Box<T> class.")]
    public Box<int> ClassBoxing() => new() { Value = int.MaxValue };

    [Benchmark(Description = "Unboxing performed by the runtime.")]
    public int RuntimeUnboxing() => (int)@object;

    [Benchmark(Description = "Unboxing performed by the Box<T> class.")]
    public int ClassUnboxing() => box;

    [Benchmark(Description = "Runtime boxing in a collection.")]
    public object[] RuntimeBoxingCollection()
    {
        object[] objects = new object[100];
        for (int index = 0; index < 100; index++) @objects[index] = index;
        return objects;
    }

    [Benchmark(Description = "Box<T> class implicit boxing in a collection.")]
    public object[] ClassBoxingCollection()
    {
        object[] objects = new object[100];
        for (int index = 0; index < 100; index++) @objects[index] = new Box<int>() { Value = index };
        return objects;
    }

    [Benchmark(Description = "Box<T> class explicit boxing in a collection.")]
    public Box<int>[] ClassBoxingExplicitCollection()
    {
        Box<int>[] objects = new Box<int>[100];
        for (int index = 0; index < 100; index++) @objects[index] = new Box<int>() { Value = index };
        return objects;
    }
}

Benchmarks.txt

.NET Framework

| Method                                          | Mean        | Error     | StdDev    | Gen0   | Gen1   | Allocated |
|------------------------------------------------ |------------:|----------:|----------:|-------:|-------:|----------:|
| 'Boxing performed by the runtime.'              |   1.7105 ns | 0.0566 ns | 0.0501 ns | 0.0038 |      - |      24 B |
| 'Boxing performed by the Box<T> class.'         |   1.4196 ns | 0.0831 ns | 0.0889 ns | 0.0038 |      - |      24 B |
| 'Unboxing performed by the runtime.'            |   0.2887 ns | 0.0009 ns | 0.0008 ns |      - |      - |         - |
| 'Unboxing performed by the Box<T> class.'       |   0.0053 ns | 0.0002 ns | 0.0002 ns |      - |      - |         - |
| 'Runtime boxing in a collection.'               | 408.6101 ns | 1.3932 ns | 1.0877 ns | 0.5136 | 0.0057 |    3233 B |
| 'Box<T> class implicit boxing in a collection.' | 410.4538 ns | 4.1383 ns | 3.6685 ns | 0.5136 | 0.0057 |    3233 B |
| 'Box<T> class explicit boxing in a collection.' | 368.2353 ns | 3.4627 ns | 3.2390 ns | 0.5136 | 0.0057 |    3233 B |

.NET 8

| Method                                          | Mean        | Error     | StdDev    | Median      | Gen0   | Gen1   | Allocated |
|------------------------------------------------ |------------:|----------:|----------:|------------:|-------:|-------:|----------:|
| 'Boxing performed by the runtime.'              |   3.2346 ns | 0.1169 ns | 0.2734 ns |   3.0730 ns | 0.0029 |      - |      24 B |
| 'Boxing performed by the Box<T> class.'         |   2.8419 ns | 0.0092 ns | 0.0086 ns |   2.8373 ns | 0.0029 |      - |      24 B |
| 'Unboxing performed by the runtime.'            |   0.4266 ns | 0.0005 ns | 0.0004 ns |   0.4267 ns |      - |      - |         - |
| 'Unboxing performed by the Box<T> class.'       |   0.0000 ns | 0.0000 ns | 0.0000 ns |   0.0000 ns |      - |      - |         - |
| 'Runtime boxing in a collection.'               | 350.8327 ns | 1.3512 ns | 1.2640 ns | 351.1452 ns | 0.3853 | 0.0043 |    3224 B |
| 'Box<T> class implicit boxing in a collection.' | 348.1842 ns | 1.4172 ns | 1.1834 ns | 348.5104 ns | 0.3853 | 0.0043 |    3224 B |
| 'Box<T> class explicit boxing in a collection.' | 341.9604 ns | 1.8653 ns | 1.6536 ns | 342.5757 ns | 0.3853 | 0.0043 |    3224 B |

System.Box.cs

namespace System;

public sealed class Box<T> where T : struct
{
    public T Value;

    public static implicit operator T(Box<T> _) => _.Value;
}