StringExtensions for Memory<T> type

BenchmarkResults.md

BenchmarkDotNet=v0.11.5, OS=Windows 10.0.18362
Intel Core i7-8850H CPU 2.60GHz (Coffee Lake), 1 CPU, 12 logical and 6 physical cores
.NET Core SDK=3.0.100
  [Host]     : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), 64bit RyuJIT
  DefaultJob : .NET Core 3.0.0 (CoreCLR 4.700.19.46205, CoreFX 4.700.19.46214), 64bit RyuJIT

Method	Mean	Error	StdDev	Gen 0	Gen 1	Gen 2	Allocated
StandardWordCounter	42.14 us	0.2934 us	0.2601 us	14.2822	2.8076	-	67376 B
StringSplitReturnIEnumerable	44.51 us	0.3816 us	0.3383 us	-	-	-	88 B
StringSplitPassDelegate	28.36 us	0.2781 us	0.2602 us	-	-	-	-
Raw	16.34 us	0.3226 us	0.3716 us	-	-	-	-

SplitWordBenchmark.cs

using BenchmarkDotNet.Attributes;
using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text;

[MemoryDiagnoser]
public class SplitWordBenchmarks
{
    [GlobalSetup]
    public void Initialize()
    {
        sentence = File.ReadAllText(@"input.txt");
    }

    public string sentence { get; set; }

    [Benchmark]
    public void StandardWordCounter()
    {
        string[] words = sentence.Split(' ');

        foreach (var word in words)
        {
            
        }
    }

    [Benchmark]
    public void StringSplitReturnIEnumerable()
    {
        var readonlyData = sentence.SplitEx(' ');
        foreach (var item in readonlyData)
        {

        }
    }

    [Benchmark]
    public void StringSplitPassDelegate()
    {
        sentence.SplitExByAction<object>(' ', null, (state, span) =>
        {

        });
    }
    
    [Benchmark]
    public void Raw()
    {
            char split = ' ';
            ReadOnlySpan<char> span = sentence.AsSpan();
            int oldIndex = 0;
            for (int i = 0; i < span.Length; i++)
            {
                if (split == span[i])
                {
                    var slicedSpan = span.Slice(oldIndex, i - oldIndex + 1);
                    oldIndex = i + 1;
                    // Do something with the slicedSpan
                }
            }
    }

}

StringExtensions.cs

public static class StringExtensions
{
    public static IEnumerable<ReadOnlyMemory<char>> SplitEx(this string input, char split)
    {
        ReadOnlyMemory<char> span = input.AsMemory();
        int oldIndex = 0;
        for (int i = 0; i < span.Length; i++)
        {
            if (split == span.Span[i])
            {
                var slicedMemory = span.Slice(oldIndex, i - oldIndex + 1);
                oldIndex = i + 1;
                yield return slicedMemory;
            }
        }
    }

    public static void SplitExByAction<T>(this string input, char split, T state, Action<T, ReadOnlyMemory<char>> action)
    {
        ReadOnlyMemory<char> span = input.AsMemory();
        int oldIndex = 0;
        for (int i = 0; i < span.Length; i++)
        {
            if (split == span.Span[i])
            {
                var slicedMemory = span.Slice(oldIndex, i - oldIndex + 1);
                oldIndex = i + 1;
                action(state, slicedMemory);
            }
        }
    }
}