wip

src/CsvHelper/Configuration/ConfigurationFunctions.cs

@@ -180,11 +180,18 @@ public static string GetDynamicPropertyName(GetDynamicPropertyNameArgs args)
 	/// Return the detected delimiter or null if one wasn't found.
 	/// </summary>
 	/// <param name="args">The args.</param>
-	public static string GetDelimiter(GetDelimiterArgs args)
+	public static char GetDelimiter(GetDelimiterArgs args)
 	{
-		var text = args.Text;
+		var text = args.Text.ToString();
 		var config = args.Configuration;
 
+		if (args.Configuration.CultureInfo.TextInfo.ListSeparator.Length > 1)
+		{
+			throw new ConfigurationException($"The CultureInfo.TextInfo.ListSeparator ");
+		}
+
+		var listSeparator = config.CultureInfo.TextInfo.ListSeparator[0];
+
 		if (config.Mode == CsvMode.RFC4180)
 		{
 			// Remove text in between pairs of quotes.
@@ -202,7 +209,7 @@ public static string GetDelimiter(GetDelimiterArgs args)
 			newLine = "\r\n|\r|\n";
 		}
 
-		var lineDelimiterCounts = new List<Dictionary<string, int>>();
+		var lineDelimiterCounts = new List<Dictionary<char, int>>();
 		while (text.Length > 0)
 		{
 			// Since all escaped text has been removed, we can reliably read line by line.
@@ -211,11 +218,11 @@ public static string GetDelimiter(GetDelimiterArgs args)
 
 			if (line.Length > 0)
 			{
-				var delimiterCounts = new Dictionary<string, int>();
+				var delimiterCounts = new Dictionary<char, int>();
 				foreach (var delimiter in config.DetectDelimiterValues)
 				{
 					// Escape regex special chars to use as regex pattern.
-					var pattern = Regex.Replace(delimiter, @"([.$^{\[(|)*+?\\])", "\\$1");
+					var pattern = Regex.Replace(delimiter.ToString(), @"([.$^{\[(|)*+?\\])", "\\$1");
 					delimiterCounts[delimiter] = Regex.Matches(line, pattern).Count;
 				}
 
@@ -247,11 +254,11 @@ orderby sum descending
 			}
 		).ToList();
 
-		string? newDelimiter = null;
-		if (delimiters.Any(x => x.Delimiter == config.CultureInfo.TextInfo.ListSeparator) && lineDelimiterCounts.Count > 1)
+		char? newDelimiter = null;
+		if (delimiters.Any(x => x.Delimiter == listSeparator) && lineDelimiterCounts.Count > 1)
 		{
 			// The culture's separator is on every line. Assume this is the delimiter.
-			newDelimiter = config.CultureInfo.TextInfo.ListSeparator;
+			newDelimiter = listSeparator;
 		}
 		else
 		{

src/CsvHelper/Configuration/CsvOptions.cs

@@ -1,11 +1,34 @@
 namespace CsvHelper.Configuration;
 
+/// <summary>
+/// Common configuration options for reading and writing CSV files.
+/// </summary>
 public abstract record CsvOptions
 {
-	public char Delimiter { get; init; } = ',';
+	/// <summary>
+	/// The mode.
+	/// See <see cref="CsvMode"/> for more details.
+	/// </summary>
+	public CsvMode Mode { get; init; }
 
+	/// <summary>
+	/// The delimiter used to separate fields.
+	/// Default is ,.
+	/// If you need a multi-character delimiter, use <see cref="ReplaceTextReader"/> to replace your newline with a single character.
+	/// </summary>
+	public char Delimiter { get; internal set; } = ',';
+
+	/// <summary>
+	/// The character used to escape characters.
+	/// Default is '"'.
+	/// </summary>
 	public char Escape { get; init; } = '\"';
 
+	/// <summary>
+	/// The newline character to use.
+	/// If not set, the parser uses one of \r\n, \r, or \n.
+	/// If you need a multi-character newline, use <see cref="ReplaceTextReader"/> to replace your newline with a single character.
+	/// </summary>
 	public char? NewLine { get; init; }
 
 	internal int BufferSize = 0x1000;

src/CsvHelper/Configuration/CsvParserOptions.cs

@@ -1,13 +1,33 @@
 namespace CsvHelper.Configuration;
 
+/// <summary>
+/// Configuration options used for <see cref="CsvParser"/>.
+/// </summary>
 public record CsvParserOptions : CsvOptions
 {
-	public CsvMode Mode { get; init; }
-
+	/// <summary>
+	/// Cache fields that are created when parsing.
+	/// Default is false.
+	/// </summary>
 	public bool CacheFields { get; init; }
 
+	/// <summary>
+	/// Strategy used for parsing.
+	/// Defaults to the highest performance your framework and CPU supports.
+	/// </summary>
 	public ParsingStrategy? ParsingStrategy { get; init; }
 
+	/// <summary>
+	/// Detect the delimiter instead of using the delimiter from configuration.
+	/// Default is <c>false</c>.
+	/// </summary>
+	public bool DetectDelimiter { get; init; }
+
+	/// <summary>
+	/// The function that is called when <see cref="DetectDelimiter"/> is enabled.
+	/// </summary>
+	public GetDelimiter GetDelimiter { get; set; } = ConfigurationFunctions.GetDelimiter;
+
 	internal StringCreator StringCreator = (chars, i)
 #if NET6_0_OR_GREATER || NETSTANDARD2_1_OR_GREATER
 		=> new string(chars);

src/CsvHelper/Configuration/CsvSerializerOptions.cs

@@ -1,11 +1,19 @@
 namespace CsvHelper.Configuration;
 
+/// <summary>
+/// A function that is used to determine if a field should get escaped when writing.
+/// </summary>
+/// <param name="field">The field.</param>
 public delegate bool ShouldEscape(ReadOnlySpan<char> field);
 
+/// <summary>
+/// Configuration options used for <see cref="CsvSerializer"/>.
+/// </summary>
 public record CsvSerializerOptions : CsvOptions
 {
-	public CsvMode Mode { get; init; }
-
+	/// <summary>
+	/// A function that is used to determine if a field should get escaped when writing.
+	/// </summary>
 	public ShouldEscape? ShouldEscape { get; init; }
 
 	internal CsvModeEscape ModeEscape = ModeRfc4180.Escape;

src/CsvHelper/Configuration/IParserConfiguration.cs

@@ -122,7 +122,7 @@ public interface IParserConfiguration
 	/// The delimiter used to separate fields.
 	/// Default is <see cref="TextInfo.ListSeparator"/>.
 	/// </summary>
-	string Delimiter { get; }
+	char Delimiter { get; }
 
 	/// <summary>
 	/// Detect the delimiter instead of using the delimiter from configuration.
@@ -139,7 +139,7 @@ public interface IParserConfiguration
 	/// The possible delimiter values used when detecting the delimiter.
 	/// Default is [",", ";", "|", "\t"].
 	/// </summary>
-	string[] DetectDelimiterValues { get; }
+	char[] DetectDelimiterValues { get; }
 
 	/// <summary>
 	/// The character used to escape characters.

src/CsvHelper/CsvParser.cs

@@ -1,6 +1,7 @@
 using CsvHelper.Configuration;
 using System.Buffers;
 using System.Collections.Concurrent;
+using System.Runtime.CompilerServices;
 
 namespace CsvHelper;
 
@@ -14,6 +15,8 @@ public class CsvParser : IParser, IDisposable
 	private bool isDisposed;
 	private int rowNumber;
 	private bool leaveOpen;
+	private bool detectDelimiter;
+	private bool delimiterDetected;
 
 	private CsvParserState state;
 
@@ -55,6 +58,8 @@ public CsvParser(TextReader reader, Func<CsvParserOptions, CsvParserOptions> con
 		options = configure(new CsvParserOptions());
 		options.Validate();
 
+		detectDelimiter = options.DetectDelimiter;
+
 		switch (options.Mode)
 		{
 			case CsvMode.RFC4180:
@@ -103,6 +108,16 @@ public bool MoveNext()
 				return false;
 			}
 
+			if (!delimiterDetected)
+			{
+				if (detectDelimiter)
+				{
+					options.Delimiter = options.GetDelimiter(state.buffer);
+				}
+
+				delimiterDetected = true;
+			}
+
 			state.Parse();
 			state.NextRow();
 		}
@@ -224,4 +239,15 @@ protected virtual void Dispose(bool isDisposing)
 		// Set large fields to null
 		isDisposed = true;
 	}
+
+	[MethodImpl(MethodImplOptions.AggressiveInlining)]
+	private void DetectDelimiter()
+	{
+		if (delimiterDetected || )
+		{
+			return;
+		}
+
+
+	}
 }

src/CsvHelper/CsvSerializer.cs

@@ -2,17 +2,33 @@
 
 namespace CsvHelper;
 
+/// <summary>
+/// Serializes objects into CSV records.
+/// </summary>
 public class CsvSerializer : IDisposable
 {
 	private TextWriter writer;
 	private CsvSerializerOptions options;
 	private CsvSerializerState state;
 	private bool isDisposed;
 
+	/// <summary>
+	/// Current row number.
+	/// </summary>
 	public int Row => state.row;
 
+	/// <summary>
+	/// Initializes a new instance of the <see cref="CsvSerializer"/> class.
+	/// </summary>
+	/// <param name="writer">The writer.</param>
 	public CsvSerializer(TextWriter writer) : this(writer, options => options) { }
 
+	/// <summary>
+	/// Initializes a new instance of the <see cref="CsvSerializer"/> class.
+	/// </summary>
+	/// <param name="writer">The writer.</param>
+	/// <param name="configureOptions">Configure options.</param>
+	/// <exception cref="NotSupportedException"></exception>
 	public CsvSerializer(TextWriter writer, Func<CsvSerializerOptions, CsvSerializerOptions> configureOptions)
 	{
 		this.writer = writer;
@@ -38,28 +54,40 @@ public CsvSerializer(TextWriter writer, Func<CsvSerializerOptions, CsvSerializer
 		state = new CsvSerializerState(writer, options);
 	}
 
+	/// <summary>
+	/// Writes the given field.
+	/// </summary>
+	/// <param name="field">The field to write.</param>
 	public void Write(ReadOnlySpan<char> field)
 	{
 		state.Write(field);
 	}
 
+	/// <summary>
+	/// Moves to the next record.
+	/// </summary>
 	public void MoveNext()
 	{
 		state.MoveNext();
 	}
 
+	/// <summary>
+	/// Flushes the buffer to the writer.
+	/// </summary>
 	public void Flush()
 	{
 		state.Flush();
 	}
 
+	/// <inheritdoc />
 	public void Dispose()
 	{
 		// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
 		Dispose(isDisposing: true);
 		GC.SuppressFinalize(this);
 	}
 
+	/// <inheritdoc />
 	protected virtual void Dispose(bool isDisposing)
 	{
 		if (isDisposed)

src/CsvHelper/Delegates/GetDelimiter.cs

@@ -2,27 +2,26 @@
 // This file is a part of CsvHelper and is dual licensed under MS-PL and Apache 2.0.
 // See LICENSE.txt for details or visit http://www.opensource.org/licenses/ms-pl.html for MS-PL and http://opensource.org/licenses/Apache-2.0 for Apache 2.0.
 // https://github.com/JoshClose/CsvHelper
-using CsvHelper.Configuration;
 
-namespace CsvHelper.Delegates;
+namespace CsvHelper.Configuration;
 
 /// <summary>
 /// Function that resolves the delimiter from the given text.
 /// Returns null if no delimiter is found.
 /// </summary>
 /// <param name="args"></param>
 /// <returns></returns>
-public delegate string GetDelimiter(GetDelimiterArgs args);
+public delegate char GetDelimiter(GetDelimiterArgs args);
 
 /// <summary>
 /// GetDelimiter args.
 /// </summary>
-public readonly struct GetDelimiterArgs
+public readonly ref struct GetDelimiterArgs
 {
 	/// <summary>
 	/// The text to resolve the delimiter from.
 	/// </summary>
-	public readonly string Text;
+	public readonly ReadOnlySpan<char> Text;
 
 	/// <summary>
 	/// The configuration.
@@ -34,7 +33,7 @@ public readonly struct GetDelimiterArgs
 	/// </summary>
 	/// <param name="text">The text to resolve the delimiter from.</param>
 	/// <param name="configuration">The configuration.</param>
-	public GetDelimiterArgs(string text, IParserConfiguration configuration)
+	public GetDelimiterArgs(ReadOnlySpan<char> text, IParserConfiguration configuration)
 	{
 		Text = text;
 		Configuration = configuration;

src/CsvHelper/IParser.cs

@@ -5,7 +5,7 @@
 namespace CsvHelper;
 
 /// <summary>
-/// Defines functionality used the parse a CSV file.
+/// Defines functionality used the parse records.
 /// </summary>
 public interface IParser : IDisposable
 {

src/CsvHelper/ISerializer.cs

@@ -0,0 +1,28 @@
+namespace CsvHelper;
+
+/// <summary>
+/// Defines functionality used to serialize records.
+/// </summary>
+public interface ISerializer : IDisposable
+{
+	/// <summary>
+	/// Current row number.
+	/// </summary>
+	int Row { get; }
+
+	/// <summary>
+	/// Writes the given field.
+	/// </summary>
+	/// <param name="field">The field to write.</param>
+	void Write(ReadOnlySpan<char> field);
+
+	/// <summary>
+	/// Moves to the next record.
+	/// </summary>
+	void MoveNext();
+
+	/// <summary>
+	/// Flushes the buffer to the writer.
+	/// </summary>
+	void Flush();
+}

src/CsvHelper/TypeConversion/IEnumerableConverter.cs

@@ -19,7 +19,7 @@ public class IEnumerableConverter : DefaultTypeConverter
 	/// <param name="row"></param>
 	/// <param name="memberMapData"></param>
 	/// <returns>The string representation of the object.</returns>
-	public override string? ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
+	public override ReadOnlySpan<char> ConvertToString(object? value, IWriterRow row, MemberMapData memberMapData)
 	{
 		var list = value as IEnumerable;
 		if (list == null)