Add interface providing read-only access to a policy registry (#283)

* Add interface providing read-only access to a policy registry

Adds an interface providing read-only access to a policy registry. Useful to prevent consumers changing policies in registry; for example to enforce separation of population of policy registry from usage.

* Add IReadOnlyPolicyRegistrySpecs

CHANGELOG.md

@@ -1,6 +1,7 @@
 ## 5.3.0
 - Fix ExecuteAndCapture() usage with PolicyWrap   
 - Allow Fallback delegates to take execution Context
+- Provide IReadOnlyPolicyRegistry interface
 
 ## 5.2.0
 - Add PolicyRegistry for storing and retrieving policies.

README.md

@@ -734,7 +734,7 @@ registry["StandardHttpResilience"] = myStandardHttpResiliencePolicy;
 // Pass the registry instance to usage sites by DI, perhaps
 public class MyServiceGateway 
 {
-    public void MyServiceGateway(..., IPolicyRegistry<string> registry, ...)
+    public void MyServiceGateway(..., IReadOnlyPolicyRegistry<string> registry, ...)
     {
        ...
     } 
@@ -905,6 +905,7 @@ For details of changes by release see the [change log](https://github.com/App-vN
 * [@reisenberger](https://github.com/reisenberger) - Add mutable Context and extra overloads taking Context.  Allows different parts of a policy execution to exchange data via the mutable Context travelling with each execution.
 * [@ankitbko](https://github.com/ankitbko) - Add PolicyRegistry for storing and retrieving policies.
 * [@reisenberger](https://github.com/reisenberger) - Add interfaces by policy type and execution type.
+* [@seanfarrow](https://github.com/SeanFarrow) - Add IReadOnlyPolicyRegistry interface.
 
 # Sample Projects
 

src/Polly.Net40Async.nuspec

@@ -19,6 +19,7 @@
      ---------------------
      - Fix ExecuteAndCapture() usage with PolicyWrap   
      - Allow Fallback delegates to take execution Context
+     - Provide IReadOnlyPolicyRegistry interface
 
      5.2.0
      ---------------------

src/Polly.Shared/Polly.Shared.projitems

@@ -77,6 +77,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)PolicyBuilder.OrSyntax.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)PolicyResult.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Policy.TResult.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Registry\IReadOnlyPolicyRegistry.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Registry\PolicyRegistry.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Registry\IPolicyRegistry.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)ResultPredicate.cs" />

src/Polly.Shared/Registry/IPolicyRegistry.cs

@@ -8,7 +8,7 @@ namespace Polly.Registry
     /// Represents a collection of policies keyed by <typeparamref name="TKey"/>.
     /// </summary>
     /// <typeparam name="TKey">The type of keys in the policy registry.</typeparam>
-    public interface IPolicyRegistry<in TKey> 
+    public interface IPolicyRegistry<in TKey> : IReadOnlyPolicyRegistry<TKey>
     {
         /// <summary>
         /// Adds an element with the provided key and policy to the registry.
@@ -21,49 +21,15 @@ public interface IPolicyRegistry<in TKey>
         void Add<TPolicy>(TKey key, TPolicy policy) where TPolicy : IsPolicy;
 
         /// <summary>
-        /// Gets of sets the <see cref="IsPolicy"/> with the specified key.
-        /// <remarks>To retrieve a policy directly as a particular Policy type or Policy interface (avoiding a cast), use the <see cref="Get{TPolicy}"/> method.</remarks>
+        /// Gets or sets the <see cref="IsPolicy"/> with the specified key.
+        /// <remarks>To retrieve a policy directly as a particular Policy type or Policy interface (avoiding a cast), use the <see cref="IReadOnlyPolicyRegistry{TKey}.Get{TPolicy}"/> method.</remarks>
         /// </summary>
         /// <param name="key">The key of the value to get or set.</param>
         /// <exception cref="T:System.ArgumentNullException"><paramref name="key" /> is null.</exception>
         /// <exception cref="KeyNotFoundException">The given key was not present in the dictionary.</exception>
         /// <returns>The value associated with the specified key.</returns>
-        IsPolicy this[TKey key] { get; set; }
-
-        /// <summary>
-        /// Gets the policy stored under the provided key, casting to <typeparamref name="TPolicy"/>.
-        /// </summary>
-        /// <typeparam name="TPolicy">The type of Policy.</typeparam>
-        /// <returns>The policy stored in the registry under the given key.</returns>
-        /// <exception cref="ArgumentNullException"><paramref name="key"/> is null.</exception>
-        TPolicy Get<TPolicy>(TKey key) where TPolicy : IsPolicy;
-
-        /// <summary>
-        /// Gets the policy stored under the provided key, casting to <typeparamref name="TPolicy"/>.
-        /// </summary>
-        /// <param name="key">The key of the policy to get.</param>
-        /// <param name="policy">
-        /// This method returns the policy associated with the specified <paramref name="key"/>, if the
-        /// key is found; otherwise null.
-        /// This parameter is passed uninitialized.
-        /// </param>
-        /// <typeparam name="TPolicy">The type of Policy.</typeparam>
-        /// <returns>True if Policy exists for the provided Key. False otherwise.</returns>
-        bool TryGet<TPolicy>(TKey key, out TPolicy policy) where TPolicy : IsPolicy;
-
-        /// <summary>
-        /// Total number of policies in the registry.
-        /// </summary>
-        int Count { get; }
-
-        /// <summary>
-        /// Determines whether the specified <paramref name="key"/> exists.
-        /// </summary>
-        /// <param name="key">The Key to locate in the registry</param>
-        /// <returns>True if <paramref name="key"/> exists otherwise false</returns>
-        /// <exception cref="ArgumentNullException"><paramref name="key"/> is null</exception>
-        bool ContainsKey(TKey key);
-
+        new IsPolicy this[TKey key] { get; set; }
+
         /// <summary>
         /// Removes the specified <see cref="Polly.Policy"/> from the registry.
         /// </summary>

src/Polly.Shared/Registry/IReadOnlyPolicyRegistry.cs

@@ -0,0 +1,57 @@
+using System;
+using System.Collections.Generic;
+using Polly;
+
+namespace Polly.Registry
+{
+    /// <summary>
+    /// Represents a read-only collection of policies keyed by <typeparamref name="TKey"/>.
+    /// </summary>
+    /// <typeparam name="TKey">The type of keys in the policy registry.</typeparam>
+    public interface IReadOnlyPolicyRegistry<in TKey>
+    {
+        /// <summary>
+        /// Gets the <see cref="IsPolicy"/> with the specified key.
+        /// <remarks>To retrieve a policy directly as a particular Policy type or Policy interface (avoiding a cast), use the <see cref="Get{TPolicy}"/> method.</remarks>
+        /// </summary>
+        /// <param name="key">The key of the value to get or set.</param>
+        /// <exception cref="T:System.ArgumentNullException"><paramref name="key" /> is null.</exception>
+        /// <exception cref="KeyNotFoundException">The given key was not present in the dictionary.</exception>
+        /// <returns>The value associated with the specified key.</returns>
+        IsPolicy this[TKey key] { get; }
+
+        /// <summary>
+        /// Gets the policy stored under the provided key, casting to <typeparamref name="TPolicy"/>.
+        /// </summary>
+        /// <typeparam name="TPolicy">The type of Policy.</typeparam>
+        /// <returns>The policy stored in the registry under the given key.</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="key"/> is null.</exception>
+        TPolicy Get<TPolicy>(TKey key) where TPolicy : IsPolicy;
+
+        /// <summary>
+        /// Gets the policy stored under the provided key, casting to <typeparamref name="TPolicy"/>.
+        /// </summary>
+        /// <param name="key">The key of the policy to get.</param>
+        /// <param name="policy">
+        /// This method returns the policy associated with the specified <paramref name="key"/>, if the
+        /// key is found; otherwise null.
+        /// This parameter is passed uninitialized.
+        /// </param>
+        /// <typeparam name="TPolicy">The type of Policy.</typeparam>
+        /// <returns>True if Policy exists for the provided Key. False otherwise.</returns>
+        bool TryGet<TPolicy>(TKey key, out TPolicy policy) where TPolicy : IsPolicy;
+
+        /// <summary>
+        /// Total number of policies in the registry.
+        /// </summary>
+        int Count { get; }
+
+        /// <summary>
+        /// Determines whether the specified <paramref name="key"/> exists.
+        /// </summary>
+        /// <param name="key">The Key to locate in the registry</param>
+        /// <returns>True if <paramref name="key"/> exists otherwise false</returns>
+        /// <exception cref="ArgumentNullException"><paramref name="key"/> is null</exception>
+        bool ContainsKey(TKey key);
+    }
+}

src/Polly.SharedSpecs/Polly.SharedSpecs.projitems

@@ -53,6 +53,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)PolicyTResultAsyncSpecs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)PolicyTResultSpecs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Registry\PolicyRegistrySpecs.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)Registry\IReadOnlyPolicyRegistrySpecs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Retry\RetryAsyncSpecs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Retry\RetryForeverAsyncSpecs.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Retry\RetryForeverSpecs.cs" />