关于 ReadOnlySpan<T>

using System;
using System.Linq;

namespace BenchmarkAndSpanExample
{
    public class NameParser
    {
        public string GetLastName(string fullName)
        {
            var names = fullName.Split(" ");

            var lastName = names.LastOrDefault();

            return lastName ?? string.Empty;
        }

        public string GetLastNameUsingSubstring(string fullName)
        {
            var lastSpaceIndex = fullName.LastIndexOf(" ", StringComparison.Ordinal);

            return lastSpaceIndex == -
                ? string.Empty
                : fullName.Substring(lastSpaceIndex + );
        }

        public ReadOnlySpan<char> GetLastNameWithSpan(ReadOnlySpan<char> fullName)
        {
            var lastSpaceIndex = fullName.LastIndexOf(' ');
            return lastSpaceIndex == -
                ? ReadOnlySpan<char>.Empty
                : fullName.Slice(lastSpaceIndex + );
        }
    }
}

using BenchmarkDotNet.Attributes;
using BenchmarkDotNet.Order;

namespace BenchmarkAndSpanExample
{
    [RankColumn]
    [Orderer(SummaryOrderPolicy.FastestToSlowest)]
    [MemoryDiagnoser]
    public class NameParserBenchmarks
    {
        private const string FullName = "Steve J Gordon";
        private static readonly NameParser Parser = new NameParser();

        [Benchmark(Baseline = true)]
        public void GetLastName()
        {
            Parser.GetLastName(FullName);
        }

        [Benchmark]
        public void GetLastNameUsingSubstring()
        {
            Parser.GetLastNameUsingSubstring(FullName);
        }

        [Benchmark]
        public void GetLastNameWithSpan()
        {
            Parser.GetLastNameWithSpan(FullName);
        }
    }
}

    public class Program
    {
        public static void Main(string[] args)
        {
            var summary = BenchmarkRunner.Run<NameParserBenchmarks>();
        }
    }