Program.cs

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Running;

namespace SpanBench
{
    class Program
    {
        static void Main(string[] args)
        {
            //BenchmarkRunner.Run<BenchmarkDemo1>();
            //BenchmarkRunner.Run<BenchmarkDemo2>();
            //BenchmarkRunner.Run<Benchmark3>();
            BenchmarkRunner.Run<BenchmarkStackHeap>();
        }
    }

    [MemoryDiagnoser]
    public class BenchmarkDemo1
    {
        private int[] _myArray;

        [Params(100, 1000, 10000)]
        public int Size { get; set; }

        [GlobalSetup]
        public void SetUp()
        {
            _myArray = new int[Size];
            for (int index = 0; index < Size; index++)
            {
                _myArray[index] = index;
            }
        }

        [Benchmark(Baseline = true)]
        public int[] Original()
        {
            return _myArray.Skip(Size / 2).Take(Size / 4).ToArray();
        }

        [Benchmark]
        public int[] ArrayCopy()
        {
            var copy = new int[Size / 4];
            Array.Copy(_myArray, Size / 2, copy, 0, Size / 4);
            return copy;
        }

        [Benchmark]
        public Span<int> Span()
        {
            return _myArray.AsSpan().Slice(Size / 2, Size / 4);
        }
    }

    [MemoryDiagnoser]
    public class BenchmarkDemo2
    {
        private static readonly string _dateString = "01 05 1991";

        [Benchmark(Baseline = true)]
        public DateTime Original()
        {
            var day = _dateString.Substring(0, 2);
            var month = _dateString.Substring(3, 2);
            var year = _dateString.Substring(6);
            return new DateTime(int.Parse(year), int.Parse(month), int.Parse(day));
        }

        [Benchmark]
        public DateTime Span()
        {
            ReadOnlySpan<char> dateSpan = _dateString;
            var day = dateSpan.Slice(0, 2);
            var month = dateSpan.Slice(3, 2);
            var year = dateSpan.Slice(6);
            return new DateTime(int.Parse(year), int.Parse(month), int.Parse(day));
        }
    }

    [MemoryDiagnoser]
    public class Benchmark3
    {
        private int[] _myArray;

        [Params(100, 1000, 10000)]
        public int Size { get; set; }

        [GlobalSetup]
        public void SetUp()
        {
            _myArray = new int[Size];
            for (int index = 0; index < Size; index++)
            {
                _myArray[index] = index;
            }
        }

        [Benchmark(Baseline = true)]
        public int[] GetArray()
            => _myArray;

        [Benchmark]
        public Span<int> GetSpan()
            => _myArray.AsSpan();
    }

    [MemoryDiagnoser]
    public class BenchmarkStackHeap
    {
        [Params(100, 1000, 10000)]
        public int Size { get; set; }

        public void Fill(Span<int> a)
        {
            for (int index = 0; index < Size; index++)
            {
                a[index] = index;
            }
        }

        [Benchmark(Baseline = true)]
        public void SpanStack()
        {
            Span<int> a = stackalloc int[Size];
            Fill(a);
        }

        [Benchmark]
        public void SpanHeap()
        {
            Span<int> a = new int[Size];
            Fill(a);
        }
    }
}