Add Initialize<TOptions>

src/Microsoft.Extensions.Options/IConfigureOptions.cs

@@ -5,6 +5,7 @@ namespace Microsoft.Extensions.Options
 {
     /// <summary>
     /// Represents something that configures the TOptions type.
+    /// Note: These are run before all <see cref="IInitializeOptions{TOptions}"/>.
     /// </summary>
     /// <typeparam name="TOptions"></typeparam>
     public interface IConfigureOptions<in TOptions> where TOptions : class

src/Microsoft.Extensions.Options/IInitializeOptions.cs

@@ -0,0 +1,20 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Represents something that initializes the TOptions type.
+    /// Note: These are run after all <see cref="IConfigureOptions{TOptions}"/>.
+    /// </summary>
+    /// <typeparam name="TOptions"></typeparam>
+    public interface IInitializeOptions<in TOptions> where TOptions : class
+    {
+        /// <summary>
+        /// Invoked to initialize a TOptions instance.
+        /// </summary>
+        /// <param name="name">The name of the options instance being initialized.</param>
+        /// <param name="options">The options instance to initialize.</param>
+        void Initialize(string name, TOptions options);
+    }
+}

src/Microsoft.Extensions.Options/InitializeOptions.cs

@@ -0,0 +1,54 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+
+namespace Microsoft.Extensions.Options
+{
+    /// <summary>
+    /// Implementation of <see cref="IInitializeOptions{TOptions}"/>.
+    /// </summary>
+    /// <typeparam name="TOptions"></typeparam>
+    public class InitializeOptions<TOptions> : IInitializeOptions<TOptions> where TOptions : class
+    {
+        /// <summary>
+        /// Creates a new instance of <see cref="InitializeOptions{TOptions}"/>.
+        /// </summary>
+        /// <param name="name">The name of the options.</param>
+        /// <param name="action">The action to register.</param>
+        public InitializeOptions(string name, Action<TOptions> action)
+        {
+            Name = name;
+            Action = action;
+        }
+
+        /// <summary>
+        /// The options name.
+        /// </summary>
+        public string Name { get; }
+
+        /// <summary>
+        /// The initialization action.
+        /// </summary>
+        public Action<TOptions> Action { get; }
+
+        /// <summary>
+        /// Invokes the registered initialization Action if the name matches.
+        /// </summary>
+        /// <param name="name"></param>
+        /// <param name="options"></param>
+        public virtual void Initialize(string name, TOptions options)
+        {
+            if (options == null)
+            {
+                throw new ArgumentNullException(nameof(options));
+            }
+
+            // Null name is used to initialize all named options.
+            if (Name == null || name == Name)
+            {
+                Action?.Invoke(options);
+            }
+        }
+    }
+}

src/Microsoft.Extensions.Options/OptionsFactory.cs

@@ -12,14 +12,17 @@ namespace Microsoft.Extensions.Options
     public class OptionsFactory<TOptions> : IOptionsFactory<TOptions> where TOptions : class, new()
     {
         private readonly IEnumerable<IConfigureOptions<TOptions>> _setups;
+        private readonly IEnumerable<IInitializeOptions<TOptions>> _initializers;
 
         /// <summary>
         /// Initializes a new instance with the specified options configurations.
         /// </summary>
         /// <param name="setups">The configuration actions to run.</param>
-        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups)
+        /// <param name="initializers">The initialization actions to run.</param>
+        public OptionsFactory(IEnumerable<IConfigureOptions<TOptions>> setups, IEnumerable<IInitializeOptions<TOptions>> initializers)
         {
             _setups = setups;
+            _initializers = initializers;
         }
 
         public TOptions Create(string name)
@@ -31,11 +34,15 @@ public TOptions Create(string name)
                 {
                     namedSetup.Configure(name, options);
                 }
-                else
+                else if (name == Options.DefaultName)
                 {
                     setup.Configure(options);
                 }
             }
+            foreach (var init in _initializers)
+            {
+                init.Initialize(name, options);
+            }
             return options;
         }
     }

src/Microsoft.Extensions.Options/OptionsServiceCollectionExtensions.cs

@@ -34,6 +34,7 @@ public static IServiceCollection AddOptions(this IServiceCollection services)
 
         /// <summary>
         /// Registers an action used to configure a particular type of options.
+        /// Note: These are run before all <seealso cref="Initialize{TOptions}(IServiceCollection, Action{TOptions})"/>.
         /// </summary>
         /// <typeparam name="TOptions">The options type to be configured.</typeparam>
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
@@ -44,6 +45,7 @@ public static IServiceCollection Configure<TOptions>(this IServiceCollection ser
 
         /// <summary>
         /// Registers an action used to configure a particular type of options.
+        /// Note: These are run before all <seealso cref="Initialize{TOptions}(IServiceCollection, Action{TOptions})"/>.
         /// </summary>
         /// <typeparam name="TOptions">The options type to be configured.</typeparam>
         /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
@@ -67,7 +69,62 @@ public static IServiceCollection Configure<TOptions>(this IServiceCollection ser
             return services;
         }
 
+        /// <summary>
+        /// Registers an action used to configure all instances of a particular type of options.
+        /// </summary>
+        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
+        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
+        /// <param name="configureOptions">The action used to configure the options.</param>
+        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
         public static IServiceCollection ConfigureAll<TOptions>(this IServiceCollection services, Action<TOptions> configureOptions) where TOptions : class
             => services.Configure(name: null, configureOptions: configureOptions);
+
+        /// <summary>
+        /// Registers an action used to initialize a particular type of options.
+        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
+        /// </summary>
+        /// <typeparam name="TOptions">The options type to be Initialized.</typeparam>
+        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
+        /// <param name="initializeOptions">The action used to initialize the options.</param>
+        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
+        public static IServiceCollection Initialize<TOptions>(this IServiceCollection services, Action<TOptions> initializeOptions) where TOptions : class
+            => services.Initialize(Options.Options.DefaultName, initializeOptions);
+
+        /// <summary>
+        /// Registers an action used to initialize a particular type of options.
+        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
+        /// </summary>
+        /// <typeparam name="TOptions">The options type to be initialized.</typeparam>
+        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
+        /// <param name="name">The name of the options instance.</param>
+        /// <param name="initializeOptions">The action used to initialize the options.</param>
+        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
+        public static IServiceCollection Initialize<TOptions>(this IServiceCollection services, string name, Action<TOptions> initializeOptions)
+            where TOptions : class
+        {
+            if (services == null)
+            {
+                throw new ArgumentNullException(nameof(services));
+            }
+
+            if (initializeOptions == null)
+            {
+                throw new ArgumentNullException(nameof(initializeOptions));
+            }
+
+            services.AddSingleton<IInitializeOptions<TOptions>>(new InitializeOptions<TOptions>(name, initializeOptions));
+            return services;
+        }
+
+        /// <summary>
+        /// Registers an action used to initialize all instances of a particular type of options.
+        /// Note: These are run after all <seealso cref="Configure{TOptions}(IServiceCollection, Action{TOptions})"/>.
+        /// </summary>
+        /// <typeparam name="TOptions">The options type to be configured.</typeparam>
+        /// <param name="services">The <see cref="IServiceCollection"/> to add the services to.</param>
+        /// <param name="initializeOptions">The action used to configure the options.</param>
+        /// <returns>The <see cref="IServiceCollection"/> so that additional calls can be chained.</returns>
+        public static IServiceCollection InitializeAll<TOptions>(this IServiceCollection services, Action<TOptions> initializeOptions) where TOptions : class
+            => services.Initialize(name: null, initializeOptions: initializeOptions);
     }
 }

test/Microsoft.Extensions.Options.Test/OptionsSnapshotTest.cs

@@ -208,6 +208,107 @@ public void CanConfigureAllDefaultAndNamedOptions()
             Assert.Equal("Default1", option.Get("1").Message);
         }
 
+        [Fact]
+        public void CanConfigureAndInitializeAllDefaultAndNamedOptions()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.ConfigureAll<FakeOptions>(o => o.Message += "Default");
+            services.Configure<FakeOptions>(o => o.Message += "0");
+            services.Configure<FakeOptions>("1", o => o.Message += "1");
+            services.InitializeAll<FakeOptions>(o => o.Message += "Initialize");
+            services.Initialize<FakeOptions>(o => o.Message += "2");
+            services.Initialize<FakeOptions>("1", o => o.Message += "3");
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("DefaultInitialize", option.Get("Default").Message);
+            Assert.Equal("Default0Initialize2", option.Value.Message);
+            Assert.Equal("Default1Initialize3", option.Get("1").Message);
+        }
+
+        [Fact]
+        public void CanInitializeAllOptions()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.InitializeAll<FakeOptions>(o => o.Message = "Default");
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("Default", option.Get("1").Message);
+            Assert.Equal("Default", option.Get("2").Message);
+        }
+
+        [Fact]
+        public void CanConfigureAndInitializeAllOptions()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.ConfigureAll<FakeOptions>(o => o.Message = "D");
+            services.InitializeAll<FakeOptions>(o => o.Message += "f");
+            services.ConfigureAll<FakeOptions>(o => o.Message += "e");
+            services.InitializeAll<FakeOptions>(o => o.Message += "ault");
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("Default", option.Get("1").Message);
+            Assert.Equal("Default", option.Get("2").Message);
+        }
+
+        [Fact]
+        public void NamedSnapshotsInitializesInRegistrationOrder()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.Initialize<FakeOptions>("-", o => o.Message += "-");
+            services.InitializeAll<FakeOptions>(o => o.Message += "A");
+            services.Initialize<FakeOptions>("+", o => o.Message += "+");
+            services.InitializeAll<FakeOptions>(o => o.Message += "B");
+            services.InitializeAll<FakeOptions>(o => o.Message += "C");
+            services.Initialize<FakeOptions>("+", o => o.Message += "+");
+            services.Initialize<FakeOptions>("-", o => o.Message += "-");
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("ABC", option.Get("1").Message);
+            Assert.Equal("A+BC+", option.Get("+").Message);
+            Assert.Equal("-ABC-", option.Get("-").Message);
+        }
+
+        [Fact]
+        public void CanInitializeAllDefaultAndNamedOptions()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.InitializeAll<FakeOptions>(o => o.Message += "Default");
+            services.Initialize<FakeOptions>(o => o.Message += "0");
+            services.Initialize<FakeOptions>("1", o => o.Message += "1");
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("Default", option.Get("Default").Message);
+            Assert.Equal("Default0", option.Value.Message);
+            Assert.Equal("Default1", option.Get("1").Message);
+        }
+
+        [Fact]
+        public void CustomIConfigureOptionsShouldOnlyAffectDefaultInstance()
+        {
+            var services = new ServiceCollection().AddOptions();
+            services.AddSingleton<IConfigureOptions<FakeOptions>, CustomSetup>();
+
+            var sp = services.BuildServiceProvider();
+            var option = sp.GetRequiredService<IOptionsSnapshot<FakeOptions>>();
+            Assert.Equal("", option.Get("NotDefault").Message);
+            Assert.Equal("Stomp", option.Get(Options.DefaultName).Message);
+            Assert.Equal("Stomp", option.Value.Message);
+            Assert.Equal("Stomp", sp.GetRequiredService<IOptions<FakeOptions>>().Value.Message);
+        }
+
+        private class CustomSetup : IConfigureOptions<FakeOptions>
+        {
+            public void Configure(FakeOptions options)
+            {
+                options.Message = "Stomp";
+            }
+        }
+
         [Fact]
         public void EnsureAddOptionsLifetimes()
         {