PR #575: Replace uses of new T[0] with Array.Empty<T>

* Add the 'EmptyRefs' helper, to support Array.Empty on .NET 4.5 (ref: #501)
* Replace uses of 'new T[0]' with 'Empty.Array<T>'

Author: Numpsy

src/ICSharpCode.SharpZipLib/Core/EmptyRefs.cs

@@ -0,0 +1,17 @@
+using System;
+
+namespace ICSharpCode.SharpZipLib.Core
+{
+	internal static class Empty
+	{
+#if NET45
+		internal static class EmptyArray<T>
+		{
+			public static readonly T[] Value = new T[0];
+		}
+		public static T[] Array<T>() => EmptyArray<T>.Value;
+#else
+		public static T[] Array<T>() => System.Array.Empty<T>();
+#endif
+	}
+}

src/ICSharpCode.SharpZipLib/Encryption/ZipAESTransform.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Security.Cryptography;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.Encryption
 {
@@ -163,7 +164,7 @@ public byte[] TransformFinalBlock(byte[] inputBuffer, int inputOffset, int input
 			{
 				throw new NotImplementedException("TransformFinalBlock is not implemented and inputCount is greater than 0");
 			}
-			return new byte[0];
+			return Empty.Array<byte>();
 		}
 
 		/// <summary>

src/ICSharpCode.SharpZipLib/Tar/TarEntry.cs

@@ -1,6 +1,7 @@
 using System;
 using System.IO;
 using System.Text;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.Tar
 {
@@ -465,7 +466,7 @@ public TarEntry[] GetDirectoryEntries()
 		{
 			if ((file == null) || !Directory.Exists(file))
 			{
-				return new TarEntry[0];
+				return Empty.Array<TarEntry>();
 			}
 
 			string[] list = Directory.GetFileSystemEntries(file);

src/ICSharpCode.SharpZipLib/Zip/ZipExtraData.cs

@@ -1,5 +1,6 @@
 using System;
 using System.IO;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.Zip
 {
@@ -521,7 +522,7 @@ public ZipExtraData(byte[] data)
 		{
 			if (data == null)
 			{
-				_data = new byte[0];
+				_data = Empty.Array<byte>();
 			}
 			else
 			{
@@ -552,7 +553,7 @@ public void Clear()
 		{
 			if ((_data == null) || (_data.Length != 0))
 			{
-				_data = new byte[0];
+				_data = Empty.Array<byte>();
 			}
 		}
 

src/ICSharpCode.SharpZipLib/Zip/ZipFile.cs

@@ -539,7 +539,7 @@ public ZipFile(Stream stream, bool leaveOpen)
 			}
 			else
 			{
-				entries_ = new ZipEntry[0];
+				entries_ = Empty.Array<ZipEntry>();
 				isNewArchive_ = true;
 			}
 		}
@@ -549,7 +549,7 @@ public ZipFile(Stream stream, bool leaveOpen)
 		/// </summary>
 		internal ZipFile()
 		{
-			entries_ = new ZipEntry[0];
+			entries_ = Empty.Array<ZipEntry>();
 			isNewArchive_ = true;
 		}
 
@@ -2338,7 +2338,7 @@ private int WriteCentralDirectoryHeader(ZipEntry entry)
 				baseStream_.Write(centralExtraData, 0, centralExtraData.Length);
 			}
 
-			byte[] rawComment = (entry.Comment != null) ? Encoding.ASCII.GetBytes(entry.Comment) : new byte[0];
+			byte[] rawComment = (entry.Comment != null) ? Encoding.ASCII.GetBytes(entry.Comment) : Empty.Array<byte>();
 
 			if (rawComment.Length > 0)
 			{
@@ -3347,7 +3347,7 @@ private void DisposeInternal(bool disposing)
 			if (!isDisposed_)
 			{
 				isDisposed_ = true;
-				entries_ = new ZipEntry[0];
+				entries_ = Empty.Array<ZipEntry>();
 
 				if (IsStreamOwner && (baseStream_ != null))
 				{

src/ICSharpCode.SharpZipLib/Zip/ZipOutputStream.cs

@@ -872,7 +872,7 @@ public override void Finish()
 				byte[] entryComment =
 					(entry.Comment != null) ?
 					ZipStrings.ConvertToArray(entry.Flags, entry.Comment) :
-					new byte[0];
+					Empty.Array<byte>();
 
 				if (entryComment.Length > 0xffff)
 				{
@@ -987,7 +987,7 @@ public override void Flush()
 		/// <summary>
 		/// Comment for the entire archive recorded in central header.
 		/// </summary>
-		private byte[] zipComment = new byte[0];
+		private byte[] zipComment = Empty.Array<byte>();
 
 		/// <summary>
 		/// Flag indicating that header patching is required for the current entry.

src/ICSharpCode.SharpZipLib/Zip/ZipStrings.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Text;
+using ICSharpCode.SharpZipLib.Core;
 
 namespace ICSharpCode.SharpZipLib.Zip
 {
@@ -174,7 +175,7 @@ public static string ConvertToStringExt(int flags, byte[] data)
 		/// <returns>Converted array</returns>
 		public static byte[] ConvertToArray(string str)
 			=> str == null
-			? new byte[0]
+			? Empty.Array<byte>()
 			: Encoding.GetEncoding(CodePage).GetBytes(str);
 
 		/// <summary>
@@ -187,7 +188,7 @@ public static byte[] ConvertToArray(string str)
 		/// <returns>Converted array</returns>
 		public static byte[] ConvertToArray(int flags, string str)
 			=> (string.IsNullOrEmpty(str))
-				? new byte[0]
+				? Empty.Array<byte>()
 				: EncodingFromFlag(flags).GetBytes(str);
 	}
 }