public class PartCounter : IPartProcessor
{
    public int Count { get; set; }

    public void OnPart(ReadOnlySpan<char> part)
    {
        Count++;
    }
}

public int CountLines(string stringToSplit)
{
    Splitter newLineSplitter = new Splitter('\n');
    PartCounter partCounter = new PartCounter();
    newLineSplitter.ExtractParts(stringToSplit, partCounter);
    return partCounter.Count;
}

public int CountLinesInFile_OnStackMemory(string fileName)
{
    StreamParser stackStreamParser = new StreamParser(new Splitter('\n'), Encoding.UTF8);
    PartCounter partCounter = new PartCounter();
    using (FileStream stream = new FileStream(fileName, FileMode.Open, FileAccess.Read))
    {
        stackStreamParser.ParseStream(stream, partCounter);
    }
    return partCounter.Count;
}

public int CountLinesInFile_OnHeap(string fileName)
{
    StreamParser arrayPoolStreamParser = new StreamParser(new Splitter('\n'), Encoding.UTF8, 1024 * 1024);
    PartCounter partCounter = new PartCounter();
    using (FileStream stream = new FileStream(fileName, FileMode.Open, FileAccess.Read))
    {
        arrayPoolStreamParser.ParseStream(stream, partCounter);
    }
    return partCounter.Count;
}

private MessageRefStruct DeserializeMessage(ReadOnlySpan<char> line)
{
    ReadOnlySpan<char> Name = ReadOnlySpan<char>.Empty;
    ReadOnlySpan<char> Value = ReadOnlySpan<char>.Empty;
    DateTime TimeStamp = DateTime.MinValue;
    int SequenceNumber = 0;

    JsonTokenizer tokenizer = new JsonTokenizer();

    tokenizer.GetNextToken(line); // object start

    tokenizer.GetNextToken(line); // Name
    Name = JsonTokenizer.GetTokenValue(tokenizer.GetNextToken(line), line);
    
    tokenizer.GetNextToken(line); // Value
    Value = JsonTokenizer.GetTokenValue(tokenizer.GetNextToken(line), line);

    tokenizer.GetNextToken(line); // TimeStamp
    TimeStamp = DateTime.Parse(JsonTokenizer.GetTokenValue(tokenizer.GetNextToken(line), line));

    tokenizer.GetNextToken(line); // SequenceNumber
    SequenceNumber = int.Parse(JsonTokenizer.GetTokenValue(tokenizer.GetNextToken(line), line));

    return new MessageRefStruct(
        Name,
        Value,
        TimeStamp,
        SequenceNumber);
}