Changed delegate ShouldQuote to include the field type.

performance/CsvHelper.Performance/Program.cs

@@ -79,7 +79,7 @@ static void WriteField(int columns = 50, int rows = 2_000_000, bool quoteAllFiel
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
 				//Delimiter = ";",
-				ShouldQuote = (field, context) => quoteAllFields,
+				ShouldQuote = (_, _, _) => quoteAllFields,
 			};
 			using (var stream = File.Create(GetFilePath()))
 			using (var writer = new StreamWriter(stream))

src/CsvHelper/Configuration/ConfigurationFunctions.cs

@@ -92,7 +92,7 @@ public static bool ReadingExceptionOccurred(CsvHelperException exception)
 		/// <param name="field">The current field.</param>
 		/// <param name="row">The current row.</param>
 		/// <returns></returns>
-		public static bool ShouldQuote(string field, IWriterRow row)
+		public static bool ShouldQuote(string field, Type fieldType, IWriterRow row)
 		{
 			var config = row.Configuration;
 

src/CsvHelper/CsvWriter.cs

@@ -57,12 +57,12 @@ public class CsvWriter : IWriter
 
 		private bool disposed;
 		private bool hasHeaderBeenWritten;
-		private bool hasRecordBeenWritten;
 		private int row = 1;
 		private int index;
 		private char[] buffer;
 		private int bufferSize;
 		private int bufferPosition;
+		private Type fieldType;
 
 		/// <inheritdoc/>
 		public virtual string[] HeaderRecord { get; private set; }
@@ -145,7 +145,9 @@ public virtual void WriteField(string field)
 				field = field.Trim();
 			}
 
-			var shouldQuoteResult = shouldQuote(field, this);
+			fieldType ??= typeof(string);
+
+			var shouldQuoteResult = shouldQuote(field, fieldType, this);
 
 			WriteField(field, shouldQuoteResult);
 		}
@@ -182,6 +184,7 @@ public virtual void WriteField(string field, bool shouldQuote)
 
 			CopyToBuffer(field);
 			index++;
+			fieldType = null;
 		}
 
 		/// <inheritdoc/>
@@ -195,7 +198,7 @@ public virtual void WriteField<T>(T field)
 		/// <inheritdoc/>
 		public virtual void WriteField<T>(T field, ITypeConverter converter)
 		{
-			var type = field == null ? typeof(string) : field.GetType();
+			var type = fieldType = field == null ? typeof(string) : field.GetType();
 			reusableMemberMapData.TypeConverter = converter;
 			if (!typeConverterOptionsCache.TryGetValue(type, out TypeConverterOptions typeConverterOptions))
 			{

src/CsvHelper/Delegates.cs

@@ -81,7 +81,7 @@ namespace CsvHelper
 	/// <summary>
 	/// Function that is used to determine if a field should get quoted when writing.
 	/// </summary>
-	public delegate bool ShouldQuote(string field, IWriterRow row);
+	public delegate bool ShouldQuote(string field, Type fieldType, IWriterRow row);
 
 	/// <summary>
 	/// Function that determines whether to skip the given record or not.

tests/CsvHelper.Tests/Configuration/ConfigurationConstructorTests.cs

@@ -78,7 +78,7 @@ public void Constructor_AllArguments_SetsProperites()
 			PrepareHeaderForMatch prepareHeaderForMatch = (header, fieldIndex) => header;
 			ReadingExceptionOccurred readingExceptionOccurred = (ex) => true;
 			ReferenceHeaderPrefix referenceHeaderPrefix = (type, memberName) => string.Empty;
-			ShouldQuote shouldQuote = (field, row) => true;
+			ShouldQuote shouldQuote = (_, _, _) => true;
 			ShouldSkipRecord shouldSkipRecord = (record) => true;
 			ShouldUseConstructorParameters shouldUseConstructorParameters = (parameterType) => true;
 

tests/CsvHelper.Tests/CsvWriterTests.cs

@@ -315,7 +315,7 @@ public void WriteRecordsAllFieldsQuotedTest()
 
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => true,
+				ShouldQuote = (_, _, _) => true,
 			};
 
 			string csv;
@@ -352,7 +352,7 @@ public void WriteRecordsNoFieldsQuotedTest()
 
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => false,
+				ShouldQuote = (_, _, _) => false,
 			};
 			string csv;
 			using (var stream = new MemoryStream())
@@ -449,7 +449,7 @@ public void WriteRecordWithQuoteAllFieldsOnAndDelimiterInFieldTest()
 		{
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => true,
+				ShouldQuote = (_, _, _) => true,
 			};
 			using (var stream = new MemoryStream())
 			using (var reader = new StreamReader(stream))
@@ -476,7 +476,7 @@ public void WriteRecordWithQuoteAllFieldsOnAndQuoteInFieldTest()
 		{
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => true,
+				ShouldQuote = (_, _, _) => true,
 			};
 			using (var stream = new MemoryStream())
 			using (var reader = new StreamReader(stream))

tests/CsvHelper.Tests/Writing/FieldTypeTests.cs

@@ -0,0 +1,42 @@
+using CsvHelper.Configuration;
+using Microsoft.VisualStudio.TestTools.UnitTesting;
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace CsvHelper.Tests.Writing
+{
+	[TestClass]
+    public class FieldTypeTests
+    {
+		[TestMethod]
+        public void Test1()
+		{
+			Type type = null;
+			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
+			{
+				ShouldQuote = (field, fieldType, row) =>
+				{
+					type = fieldType;
+					return ConfigurationFunctions.ShouldQuote(field, fieldType, row);
+				},
+			};
+			using (var writer = new StringWriter())
+			using (var csv = new CsvWriter(writer, config))
+			{
+				csv.WriteField(string.Empty);
+				Assert.AreEqual(typeof(string), type);
+
+				csv.WriteField(1);
+				Assert.AreEqual(typeof(int), type);
+
+				csv.WriteField(string.Empty);
+				Assert.AreEqual(typeof(string), type);
+			}
+		}
+    }
+}

tests/CsvHelper.Tests/Writing/SanitizationTests.cs

@@ -36,7 +36,7 @@ public void QuoteTest()
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
 				SanitizeForInjection = true,
-				ShouldQuote = (field, context) => false,
+				ShouldQuote = (_, _, _) => false,
 			};
 			using (var writer = new StringWriter())
 			using (var csv = new CsvWriter(writer, config))
@@ -73,7 +73,7 @@ public void QuoteChangeEscapeCharacterTest()
 			{
 				SanitizeForInjection = true,
 				InjectionEscapeCharacter = '\'',
-				ShouldQuote = (field, context) => false,
+				ShouldQuote = (_, _, _) => false,
 			};
 			using (var writer = new StringWriter())
 			using (var csv = new CsvWriter(writer, config))

tests/CsvHelper.Tests/Writing/ShouldQuoteTests.cs

@@ -18,7 +18,7 @@ public void QuoteAllFieldsTest()
 		{
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => true,
+				ShouldQuote = (_, _, _) => true,
 			};
 			using (var writer = new StringWriter())
 			using (var csv = new CsvWriter(writer, config))
@@ -35,7 +35,7 @@ public void QuoteNoFieldsTest()
 		{
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, context) => false,
+				ShouldQuote = (_, _, _) => false,
 			};
 			using (var writer = new StringWriter())
 			using (var csv = new CsvWriter(writer, config))
@@ -144,11 +144,11 @@ public void Test1()
 			var data = new List<(int row, int column, string field)>();
 			var config = new CsvConfiguration(CultureInfo.InvariantCulture)
 			{
-				ShouldQuote = (field, row) =>
+				ShouldQuote = (field, fieldType, row) =>
 				{
 					data.Add((row.Row, row.Index, field));
 
-					return ConfigurationFunctions.ShouldQuote(field, row);
+					return ConfigurationFunctions.ShouldQuote(field, fieldType, row);
 				},
 			};
 			using (var writer = new StringWriter())