Make fields readonly (#1451)

Added `readonly` modifier to private fields which are never changed.

---------

Co-authored-by: Lehonti Ramos <john@doe>

Author: Lehonti

src/Polly/Caching/AsyncCachePolicy.cs

@@ -80,7 +80,7 @@ public class AsyncCachePolicy<TResult> : AsyncPolicy<TResult>
     private readonly Action<Context, string, Exception>? _onCacheGetError;
     private readonly Action<Context, string, Exception>? _onCachePutError;
 
-    private IAsyncCacheProvider<TResult> _asyncCacheProvider;
+    private readonly IAsyncCacheProvider<TResult> _asyncCacheProvider;
 
     internal AsyncCachePolicy(
         IAsyncCacheProvider<TResult> asyncCacheProvider,

src/Polly/Caching/CachePolicy.cs

@@ -70,8 +70,8 @@ public class CachePolicy<TResult> : Policy<TResult>, ICachePolicy<TResult>
     private readonly Action<Context, string, Exception>? _onCacheGetError;
     private readonly Action<Context, string, Exception>? _onCachePutError;
 
-    private ISyncCacheProvider<TResult> _syncCacheProvider;
-    private ITtlStrategy<TResult> _ttlStrategy;
+    private readonly ISyncCacheProvider<TResult> _syncCacheProvider;
+    private readonly ITtlStrategy<TResult> _ttlStrategy;
     private Func<Context, string> _cacheKeyStrategy;
 
     internal CachePolicy(

src/Polly/Timeout/AsyncTimeoutPolicy.cs

@@ -43,8 +43,8 @@ protected override Task<TResult> ImplementationAsync<TResult>(
 /// <typeparam name="TResult">The return type of delegates which may be executed through the policy.</typeparam>
 public class AsyncTimeoutPolicy<TResult> : AsyncPolicy<TResult>, ITimeoutPolicy<TResult>
 {
+    private readonly TimeoutStrategy _timeoutStrategy;
     private Func<Context, TimeSpan> _timeoutProvider;
-    private TimeoutStrategy _timeoutStrategy;
     private Func<Context, TimeSpan, Task, Exception, Task> _onTimeoutAsync;
 
     internal AsyncTimeoutPolicy(

src/Polly/Timeout/TimeoutPolicy.cs

@@ -5,8 +5,8 @@
 /// </summary>
 public class TimeoutPolicy : Policy, ITimeoutPolicy
 {
+    private readonly TimeoutStrategy _timeoutStrategy;
     private Func<Context, TimeSpan> _timeoutProvider;
-    private TimeoutStrategy _timeoutStrategy;
     private Action<Context, TimeSpan, Task, Exception> _onTimeout;
 
     internal TimeoutPolicy(
@@ -36,8 +36,8 @@ protected override TResult Implementation<TResult>(Func<Context, CancellationTok
 /// </summary>
 public class TimeoutPolicy<TResult> : Policy<TResult>, ITimeoutPolicy<TResult>
 {
+    private readonly TimeoutStrategy _timeoutStrategy;
     private Func<Context, TimeSpan> _timeoutProvider;
-    private TimeoutStrategy _timeoutStrategy;
     private Action<Context, TimeSpan, Task, Exception> _onTimeout;
 
     internal TimeoutPolicy(

src/Polly/Wrap/AsyncPolicyWrap.cs

@@ -5,8 +5,8 @@
 /// </summary>
 public partial class AsyncPolicyWrap : AsyncPolicy, IPolicyWrap
 {
-    private IAsyncPolicy _outer;
-    private IAsyncPolicy _inner;
+    private readonly IAsyncPolicy _outer;
+    private readonly IAsyncPolicy _inner;
 
     /// <summary>
     /// Returns the outer <see cref="IsPolicy"/> in this <see cref="IPolicyWrap"/>
@@ -61,11 +61,11 @@ protected override Task<TResult> ImplementationAsync<TResult>(Func<Context, Canc
 /// <typeparam name="TResult">The return type of delegates which may be executed through the policy.</typeparam>
 public partial class AsyncPolicyWrap<TResult> : AsyncPolicy<TResult>, IPolicyWrap<TResult>
 {
-    private IAsyncPolicy _outerNonGeneric;
-    private IAsyncPolicy _innerNonGeneric;
+    private readonly IAsyncPolicy _outerNonGeneric;
+    private readonly IAsyncPolicy _innerNonGeneric;
 
-    private IAsyncPolicy<TResult> _outerGeneric;
-    private IAsyncPolicy<TResult> _innerGeneric;
+    private readonly IAsyncPolicy<TResult> _outerGeneric;
+    private readonly IAsyncPolicy<TResult> _innerGeneric;
 
     /// <summary>
     /// Returns the outer <see cref="IsPolicy"/> in this <see cref="IPolicyWrap{TResult}"/>

src/Polly/Wrap/PolicyWrap.cs

@@ -5,8 +5,8 @@
 /// </summary>
 public partial class PolicyWrap : Policy, IPolicyWrap
 {
-    private ISyncPolicy _outer;
-    private ISyncPolicy _inner;
+    private readonly ISyncPolicy _outer;
+    private readonly ISyncPolicy _inner;
 
     /// <summary>
     /// Returns the outer <see cref="IsPolicy"/> in this <see cref="IPolicyWrap"/>
@@ -54,11 +54,11 @@ protected override TResult Implementation<TResult>(Func<Context, CancellationTok
 /// <typeparam name="TResult">The return type of delegates which may be executed through the policy.</typeparam>
 public partial class PolicyWrap<TResult> : Policy<TResult>, IPolicyWrap<TResult>
 {
-    private ISyncPolicy _outerNonGeneric;
-    private ISyncPolicy _innerNonGeneric;
+    private readonly ISyncPolicy _outerNonGeneric;
+    private readonly ISyncPolicy _innerNonGeneric;
 
-    private ISyncPolicy<TResult> _outerGeneric;
-    private ISyncPolicy<TResult> _innerGeneric;
+    private readonly ISyncPolicy<TResult> _outerGeneric;
+    private readonly ISyncPolicy<TResult> _innerGeneric;
 
     /// <summary>
     /// Returns the outer <see cref="IsPolicy"/> in this <see cref="IPolicyWrap{TResult}"/>