More CoreLib code cleanup

src/System.Private.CoreLib/shared/Internal/Win32/RegistryKey.cs

@@ -29,7 +29,7 @@ internal sealed class RegistryKey : IDisposable
  private const int MaxKeyLength = 255;
  private const int MaxValueLength = 16383;
 
- private SafeRegistryHandle _hkey;
+ private readonly SafeRegistryHandle _hkey;
 
  private RegistryKey(SafeRegistryHandle hkey)
  {

src/System.Private.CoreLib/shared/System/AggregateException.cs

@@ -25,7 +25,7 @@ namespace System
  [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
  public class AggregateException : Exception
  {
- private ReadOnlyCollection<Exception> m_innerExceptions; // Complete set of exceptions. Do not rename (binary serialization)
+ private readonly ReadOnlyCollection<Exception> m_innerExceptions; // Complete set of exceptions. Do not rename (binary serialization)
 
  /// <summary>
  /// Initializes a new instance of the <see cref="AggregateException"/> class.
@@ -258,7 +258,7 @@ protected AggregateException(SerializationInfo info, StreamingContext context) :
  }
 
  Exception[]? innerExceptions = info.GetValue("InnerExceptions", typeof(Exception[])) as Exception[];
- if (innerExceptions == null)
+ if (innerExceptions is null)
  {
  throw new SerializationException(SR.AggregateException_DeserializationFailure);
  }

src/System.Private.CoreLib/shared/System/ArgumentException.cs

@@ -23,7 +23,7 @@ namespace System
  [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
  public class ArgumentException : SystemException
  {
- private string? _paramName;
+ private readonly string? _paramName;
 
  // Creates a new ArgumentException with its message
  // string set to the empty string.

src/System.Private.CoreLib/shared/System/ArgumentOutOfRangeException.cs

@@ -22,7 +22,7 @@ namespace System
  [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
  public class ArgumentOutOfRangeException : ArgumentException
  {
- private object? _actualValue;
+ private readonly object? _actualValue;
 
  // Creates a new ArgumentOutOfRangeException with its message
  // string set to a default message explaining an argument was out of range.

src/System.Private.CoreLib/shared/System/Array.Enumerators.cs

@@ -10,11 +10,11 @@ namespace System
 {
  internal sealed class ArrayEnumerator : IEnumerator, ICloneable
  {
- private Array array;
+ private readonly Array array;
  private int index;
- private int endIndex;
- private int startIndex; // Save for Reset.
- private int[] _indices; // The current position in a multidim array
+ private readonly int endIndex;
+ private readonly int startIndex; // Save for Reset.
+ private readonly int[] _indices; // The current position in a multidim array
  private bool _complete;
 
  internal ArrayEnumerator(Array array, int index, int count)
@@ -110,7 +110,7 @@ internal sealed class SZArrayEnumerator : IEnumerator, ICloneable
  {
  private readonly Array _array;
  private int _index;
- private int _endIndex; // Cache Array.Length, since it's a little slow.
+ private readonly int _endIndex; // Cache Array.Length, since it's a little slow.
 
  internal SZArrayEnumerator(Array array)
  {

src/System.Private.CoreLib/shared/System/Array.cs

@@ -936,9 +936,8 @@ public static int IndexOf(Array array, object? value, int startIndex, int count)
  return retVal;
 #endif
 
- object[]? objArray = array as object[];
  int endIndex = startIndex + count;
- if (objArray != null)
+ if (array is object[] objArray)
  {
  if (value == null)
  {
@@ -1120,9 +1119,8 @@ public static int LastIndexOf(Array array, object? value, int startIndex, int co
  return retVal;
 #endif
 
- object[]? objArray = array as object[];
  int endIndex = startIndex - count + 1;
- if (objArray != null)
+ if (array is object[] objArray)
  {
  if (value == null)
  {

src/System.Private.CoreLib/shared/System/AttributeUsageAttribute.cs

@@ -19,7 +19,7 @@ namespace System
  [AttributeUsage(AttributeTargets.Class, Inherited = true)]
  public sealed class AttributeUsageAttribute : Attribute
  {
- private AttributeTargets _attributeTarget = AttributeTargets.All; // Defaults to all
+ private readonly AttributeTargets _attributeTarget = AttributeTargets.All; // Defaults to all
  private bool _allowMultiple = false; // Defaults to false
  private bool _inherited = true; // Defaults to true
 

src/System.Private.CoreLib/shared/System/BadImageFormatException.cs

@@ -21,8 +21,8 @@ namespace System
  [System.Runtime.CompilerServices.TypeForwardedFrom("mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089")]
  public partial class BadImageFormatException : SystemException
  {
- private string? _fileName; // The name of the corrupt PE file.
- private string? _fusionLog; // fusion log (when applicable)
+ private readonly string? _fileName; // The name of the corrupt PE file.
+ private readonly string? _fusionLog; // fusion log (when applicable)
 
  public BadImageFormatException()
  : base(SR.Arg_BadImageFormatException)

src/System.Private.CoreLib/shared/System/Buffers/ConfigurableArrayPool.cs

@@ -74,7 +74,7 @@ public override T[] Rent(int minimumLength)
  }
 
  var log = ArrayPoolEventSource.Log;
- T[]? buffer = null;
+ T[]? buffer;
 
  int index = Utilities.SelectBucketIndex(minimumLength);
  if (index < _buckets.Length)

src/System.Private.CoreLib/shared/System/Buffers/Text/Utf8Formatter/Utf8Formatter.Date.O.cs

@@ -49,7 +49,7 @@ private static bool TryFormatDateTimeO(DateTime value, TimeSpan offset, Span<byt
  bytesWritten = bytesRequired;
 
  // Hoist most of the bounds checks on buffer.
- { var unused = destination[MinimumBytesNeeded - 1]; }
+ { _ = destination[MinimumBytesNeeded - 1]; }
 
  FormattingHelpers.WriteFourDecimalDigits((uint)value.Year, destination, 0);
  destination[4] = Utf8Constants.Minus;

src/System.Private.CoreLib/shared/System/Buffers/Text/Utf8Formatter/Utf8Formatter.Date.cs

@@ -105,23 +105,14 @@ public static bool TryFormat(DateTimeOffset value, Span<byte> destination, out i
  offset = value.Offset;
  }
 
- switch (symbol)
+ return symbol switch
  {
- case 'R':
- return TryFormatDateTimeR(value.UtcDateTime, destination, out bytesWritten);
-
- case 'l':
- return TryFormatDateTimeL(value.UtcDateTime, destination, out bytesWritten);
-
- case 'O':
- return TryFormatDateTimeO(value.DateTime, value.Offset, destination, out bytesWritten);
-
- case 'G':
- return TryFormatDateTimeG(value.DateTime, offset, destination, out bytesWritten);
-
- default:
- return FormattingHelpers.TryFormatThrowFormatException(out bytesWritten);
- }
+ 'R' => TryFormatDateTimeR(value.UtcDateTime, destination, out bytesWritten),
+ 'l' => TryFormatDateTimeL(value.UtcDateTime, destination, out bytesWritten),
+ 'O' => TryFormatDateTimeO(value.DateTime, value.Offset, destination, out bytesWritten),
+ 'G' => TryFormatDateTimeG(value.DateTime, offset, destination, out bytesWritten),
+ _ => FormattingHelpers.TryFormatThrowFormatException(out bytesWritten),
+ };
  }
 
  /// <summary>
@@ -149,23 +140,14 @@ public static bool TryFormat(DateTime value, Span<byte> destination, out int byt
  {
  char symbol = FormattingHelpers.GetSymbolOrDefault(format, 'G');
 
- switch (symbol)
+ return symbol switch
  {
- case 'R':
- return TryFormatDateTimeR(value, destination, out bytesWritten);
-
- case 'l':
- return TryFormatDateTimeL(value, destination, out bytesWritten);
-
- case 'O':
- return TryFormatDateTimeO(value, Utf8Constants.NullUtcOffset, destination, out bytesWritten);
-
- case 'G':
- return TryFormatDateTimeG(value, Utf8Constants.NullUtcOffset, destination, out bytesWritten);
-
- default:
- return FormattingHelpers.TryFormatThrowFormatException(out bytesWritten);
- }
+ 'R' => TryFormatDateTimeR(value, destination, out bytesWritten),
+ 'l' => TryFormatDateTimeL(value, destination, out bytesWritten),
+ 'O' => TryFormatDateTimeO(value, Utf8Constants.NullUtcOffset, destination, out bytesWritten),
+ 'G' => TryFormatDateTimeG(value, Utf8Constants.NullUtcOffset, destination, out bytesWritten),
+ _ => FormattingHelpers.TryFormatThrowFormatException(out bytesWritten),
+ };
  }
  }
 }

src/System.Private.CoreLib/shared/System/Buffers/Text/Utf8Formatter/Utf8Formatter.Guid.cs

@@ -117,7 +117,7 @@ public static bool TryFormat(Guid value, Span<byte> destination, out int bytesWr
  // because it may have an observable side effect (throwing).
  // We use 8 instead of 7 so that we also capture the dash if we're asked to insert one.
 
- { var unused = destination[8]; }
+ { _ = destination[8]; }
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte03, destination, 0, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte02, destination, 2, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte01, destination, 4, FormattingHelpers.HexCasing.Lowercase);
@@ -133,7 +133,7 @@ public static bool TryFormat(Guid value, Span<byte> destination, out int bytesWr
  destination = destination.Slice(8);
  }
 
- { var unused = destination[4]; }
+ { _ = destination[4]; }
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte05, destination, 0, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte04, destination, 2, FormattingHelpers.HexCasing.Lowercase);
 
@@ -147,7 +147,7 @@ public static bool TryFormat(Guid value, Span<byte> destination, out int bytesWr
  destination = destination.Slice(4);
  }
 
- { var unused = destination[4]; }
+ { _ = destination[4]; }
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte07, destination, 0, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte06, destination, 2, FormattingHelpers.HexCasing.Lowercase);
 
@@ -161,7 +161,7 @@ public static bool TryFormat(Guid value, Span<byte> destination, out int bytesWr
  destination = destination.Slice(4);
  }
 
- { var unused = destination[4]; }
+ { _ = destination[4]; }
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte08, destination, 0, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte09, destination, 2, FormattingHelpers.HexCasing.Lowercase);
 
@@ -175,7 +175,7 @@ public static bool TryFormat(Guid value, Span<byte> destination, out int bytesWr
  destination = destination.Slice(4);
  }
 
- { var unused = destination[11]; } // can't hoist bounds check on the final brace (if exists)
+ { _ = destination[11]; } // can't hoist bounds check on the final brace (if exists)
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte10, destination, 0, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte11, destination, 2, FormattingHelpers.HexCasing.Lowercase);
  FormattingHelpers.WriteHexByte(guidAsBytes.Byte12, destination, 4, FormattingHelpers.HexCasing.Lowercase);

src/System.Private.CoreLib/shared/System/Buffers/Text/Utf8Parser/Utf8Parser.Date.cs

@@ -121,26 +121,15 @@ public static bool TryParse(ReadOnlySpan<byte> source, out DateTime value, out i
  /// </exceptions>
  public static bool TryParse(ReadOnlySpan<byte> source, out DateTimeOffset value, out int bytesConsumed, char standardFormat = default)
  {
- switch (standardFormat)
+ return standardFormat switch
  {
- case 'R':
- return TryParseDateTimeOffsetR(source, NoFlipCase, out value, out bytesConsumed);
-
- case 'l':
- return TryParseDateTimeOffsetR(source, FlipCase, out value, out bytesConsumed);
-
- case 'O':
- return TryParseDateTimeOffsetO(source, out value, out bytesConsumed, out _);
-
- case default(char):
- return TryParseDateTimeOffsetDefault(source, out value, out bytesConsumed);
-
- case 'G':
- return TryParseDateTimeG(source, out DateTime _, out value, out bytesConsumed);
-
- default:
- return ParserHelpers.TryParseThrowFormatException(out value, out bytesConsumed);
- }
+ 'R' => TryParseDateTimeOffsetR(source, NoFlipCase, out value, out bytesConsumed),
+ 'l' => TryParseDateTimeOffsetR(source, FlipCase, out value, out bytesConsumed),
+ 'O' => TryParseDateTimeOffsetO(source, out value, out bytesConsumed, out _),
+ default(char) => TryParseDateTimeOffsetDefault(source, out value, out bytesConsumed),
+ 'G' => TryParseDateTimeG(source, out DateTime _, out value, out bytesConsumed),
+ _ => ParserHelpers.TryParseThrowFormatException(out value, out bytesConsumed),
+ };
  }
 
  private const uint FlipCase = 0x00000020u; // XOR mask to flip the case of a letter.

src/System.Private.CoreLib/shared/System/CLSCompliantAttribute.cs

@@ -16,7 +16,7 @@ namespace System
  [AttributeUsage(AttributeTargets.All, Inherited = true, AllowMultiple = false)]
  public sealed class CLSCompliantAttribute : Attribute
  {
- private bool _compliant;
+ private readonly bool _compliant;
 
  public CLSCompliantAttribute(bool isCompliant)
  {

src/System.Private.CoreLib/shared/System/Collections/ArrayList.cs

@@ -772,7 +772,7 @@ public virtual void TrimToSize()
  // Note this requires reimplementing half of ArrayList...
  private class IListWrapper : ArrayList
  {
- private IList _list;
+ private readonly IList _list;
 
  internal IListWrapper(IList list)
  {
@@ -983,8 +983,7 @@ public override void InsertRange(int index, ICollection c)
 
  if (c.Count > 0)
  {
- ArrayList? al = _list as ArrayList;
- if (al != null)
+ if (_list is ArrayList al)
  {
  // We need to special case ArrayList.
  // When c is a range of _list, we need to handle this in a special way.
@@ -1235,8 +1234,8 @@ public void Reset()
 
  private class SyncArrayList : ArrayList
  {
- private ArrayList _list;
- private object _root;
+ private readonly ArrayList _list;
+ private readonly object _root;
 
  internal SyncArrayList(ArrayList list)
  : base(false)
@@ -1590,8 +1589,8 @@ public override void TrimToSize()
 
  private class SyncIList : IList
  {
- private IList _list;
- private object _root;
+ private readonly IList _list;
+ private readonly object _root;
 
  internal SyncIList(IList list)
  {
@@ -1719,7 +1718,7 @@ public virtual void RemoveAt(int index)
 
  private class FixedSizeList : IList
  {
- private IList _list;
+ private readonly IList _list;
 
  internal FixedSizeList(IList l)
  {
@@ -2031,7 +2030,7 @@ public override void TrimToSize()
 
  private class ReadOnlyList : IList
  {
- private IList _list;
+ private readonly IList _list;
 
  internal ReadOnlyList(IList l)
  {
@@ -2343,12 +2342,12 @@ public override void TrimToSize()
  // made to the list while an enumeration is in progress.
  private sealed class ArrayListEnumerator : IEnumerator, ICloneable
  {
- private ArrayList _list;
+ private readonly ArrayList _list;
  private int _index;
- private int _endIndex; // Where to stop.
- private int _version;
+ private readonly int _endIndex; // Where to stop.
+ private readonly int _version;
  private object? _currentElement;
- private int _startIndex; // Save this for Reset.
+ private readonly int _startIndex; // Save this for Reset.
 
  internal ArrayListEnumerator(ArrayList list, int index, int count)
  {
@@ -2404,7 +2403,7 @@ public void Reset()
  private class Range : ArrayList
  {
  private ArrayList _baseList;
- private int _baseIndex;
+ private readonly int _baseIndex;
  private int _baseSize;
  private int _baseVersion;
 
@@ -2819,13 +2818,13 @@ public override void TrimToSize()
 
  private sealed class ArrayListEnumeratorSimple : IEnumerator, ICloneable
  {
- private ArrayList _list;
+ private readonly ArrayList _list;
  private int _index;
- private int _version;
+ private readonly int _version;
  private object? _currentElement;
- private bool _isArrayList;
+ private readonly bool _isArrayList;
  // this object is used to indicate enumeration has not started or has terminated
- private static object s_dummyObject = new object();
+ private static readonly object s_dummyObject = new object();
 
  internal ArrayListEnumeratorSimple(ArrayList list)
  {
@@ -2910,7 +2909,7 @@ public void Reset()
 
  internal class ArrayListDebugView
  {
- private ArrayList _arrayList;
+ private readonly ArrayList _arrayList;
 
  public ArrayListDebugView(ArrayList arrayList)
  {