Mark more structs as readonly (dotnet/coreclr#19557)

Signed-off-by: dotnet-bot <dotnet-bot@microsoft.com>

src/System.Private.CoreLib/shared/System/Globalization/TimeSpanParse.cs

@@ -804,7 +804,7 @@ namespace System.Globalization
                     }
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
 
@@ -932,7 +932,7 @@ namespace System.Globalization
                     }
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
 
@@ -1058,7 +1058,7 @@ namespace System.Globalization
                     }
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
 
@@ -1130,7 +1130,7 @@ namespace System.Globalization
                     }
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
 
@@ -1200,7 +1200,7 @@ namespace System.Globalization
                     }
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
 
@@ -1399,7 +1399,7 @@ namespace System.Globalization
                     ticks = -ticks;
                 }
 
-                result.parsedTimeSpan._ticks = ticks;
+                result.parsedTimeSpan = new TimeSpan(ticks);
                 return true;
             }
             else
@@ -1494,7 +1494,7 @@ namespace System.Globalization
 
             internal bool TryParse(ReadOnlySpan<char> input, ref TimeSpanResult result)
             {
-                result.parsedTimeSpan._ticks = 0;
+                result.parsedTimeSpan = default;
 
                 _str = input;
                 _len = input.Length;
@@ -1563,7 +1563,7 @@ namespace System.Globalization
                     return result.SetBadTimeSpanFailure();
                 }
 
-                result.parsedTimeSpan._ticks = time;
+                result.parsedTimeSpan = new TimeSpan(time);
                 return true;
             }
 

src/System.Private.CoreLib/shared/System/Runtime/InteropServices/HandleRef.cs

@@ -4,12 +4,12 @@
 
 namespace System.Runtime.InteropServices
 {
-    public struct HandleRef
+    public readonly struct HandleRef
     {
         // ! Do not add or rearrange fields as the EE depends on this layout.
         //------------------------------------------------------------------
-        private object _wrapper;
-        private IntPtr _handle;
+        private readonly object _wrapper;
+        private readonly IntPtr _handle;
         //------------------------------------------------------------------
 
         public HandleRef(object wrapper, IntPtr handle)

src/System.Private.CoreLib/shared/System/Runtime/Serialization/SerializationInfoEnumerator.cs

@@ -7,11 +7,11 @@ using System.Diagnostics;
 
 namespace System.Runtime.Serialization
 {
-    public struct SerializationEntry
+    public readonly struct SerializationEntry
     {
-        private string _name;
-        private object _value;
-        private Type _type;
+        private readonly string _name;
+        private readonly object _value;
+        private readonly Type _type;
 
         internal SerializationEntry(string entryName, object entryValue, Type entryType)
         {

src/System.Private.CoreLib/shared/System/SpanHelpers.BinarySearch.cs

@@ -62,11 +62,11 @@ namespace System
         }
 
         // Helper to allow sharing all code via IComparable<T> inlineable
-        internal struct ComparerComparable<T, TComparer> : IComparable<T>
+        internal readonly struct ComparerComparable<T, TComparer> : IComparable<T>
             where TComparer : IComparer<T>
         {
-            readonly T _value;
-            readonly TComparer _comparer;
+            private readonly T _value;
+            private readonly TComparer _comparer;
 
             public ComparerComparable(T value, TComparer comparer)
             {

src/System.Private.CoreLib/shared/System/Threading/AsyncLocal.cs

@@ -86,19 +86,18 @@ namespace System.Threading
         void OnValueChanged(object previousValue, object currentValue, bool contextChanged);
     }
 
-    public struct AsyncLocalValueChangedArgs<T>
+    public readonly struct AsyncLocalValueChangedArgs<T>
     {
-        public T PreviousValue { get; private set; }
-        public T CurrentValue { get; private set; }
+        public T PreviousValue { get; }
+        public T CurrentValue { get; }
 
         //
         // If the value changed because we changed to a different ExecutionContext, this is true.  If it changed
         // because someone set the Value property, this is false.
         //
-        public bool ThreadContextChanged { get; private set; }
+        public bool ThreadContextChanged { get; }
 
         internal AsyncLocalValueChangedArgs(T previousValue, T currentValue, bool contextChanged)
-            : this()
         {
             PreviousValue = previousValue;
             CurrentValue = currentValue;

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

@@ -28,7 +28,7 @@ namespace System
     // an appropriate custom ILMarshaler to keep WInRT interop scenarios enabled.
     //
     [Serializable]
-    public struct TimeSpan : IComparable, IComparable<TimeSpan>, IEquatable<TimeSpan>, IFormattable, ISpanFormattable
+    public readonly struct TimeSpan : IComparable, IComparable<TimeSpan>, IEquatable<TimeSpan>, IFormattable, ISpanFormattable
     {
         public const long TicksPerMillisecond = 10000;
         private const double MillisecondsPerTick = 1.0 / TicksPerMillisecond;
@@ -65,7 +65,7 @@ namespace System
 
         // internal so that DateTime doesn't have to call an extra get
         // method for some arithmetic operations.
-        internal long _ticks; // Do not rename (binary serialization)
+        internal readonly long _ticks; // Do not rename (binary serialization)
 
         public TimeSpan(long ticks)
         {