Added details about IEnumerable<T> into DI.

docs/core/extensions/access-by-line.txt

@@ -0,0 +1,22 @@
+snippets/configuration/dependency-injection/Program.cs: ~/docs/core/extensions/dependency-injection.md
+snippets/configuration/console-di-ienumerable/Program.cs: ~/docs/core/extensions/dependency-injection.md
+snippets/configuration/console-di-ienumerable/ExampleService.cs: ~/docs/core/extensions/dependency-injection.md
+snippets/configuration/console-json/Program.cs: ~/docs/core/extensions/configuration-providers.md
+snippets/configuration/console-xml/Program.cs: ~/docs/core/extensions/configuration-providers.md
+snippets/configuration/console-ini/Program.cs: ~/docs/core/extensions/configuration-providers.md
+snippets/configuration/console/Program.cs: ~/docs/core/extensions/configuration.md
+snippets/logging/console-formatter-simple/Program.cs: ~/docs/core/extensions/custom-log-formatter.md
+snippets/configuration/custom-provider/Program.cs: ~/docs/core/extensions/custom-configuration-provider.md
+snippets/configuration/console-custom-logging/ColorConsoleLogger.cs: ~/docs/core/extensions/custom-logging-provider.md
+snippets/configuration/console-di-disposable/Program.cs: ~/docs/core/extensions/dependency-injection-guidelines.md
+snippets/configuration/console-di/Program.cs: ~/docs/core/extensions/dependency-injection-usage.md
+snippets/configuration/console-host/Program.cs: ~/docs/core/extensions/generic-host.md
+snippets/configuration/app-lifetime/Program.cs: ~/docs/core/extensions/generic-host.md
+snippets/configuration/app-lifetime/ExampleHostedService.cs: ~/docs/core/extensions/generic-host.md
+snippets/configuration/worker-service-options/Worker.cs: ~/docs/core/extensions/high-performance-logging.md
+snippets/configuration/console/Program.cs: ~/docs/core/extensions/logging-providers.md
+snippets/configuration/worker-service/appsettings.IncludeScopes.json: ~/docs/core/extensions/logging.md
+snippets/configuration/worker-service/Worker.cs: ~/docs/core/extensions/logging.md
+snippets/configuration/console-json/appsettings.json: ~/docs/core/extensions/options.md
+snippets/configuration/console-json/TransientFaultHandlingOptions.cs: ~/docs/core/extensions/options.md
+snippets/configuration/console-json/Program.cs: ~/docs/core/extensions/options.md

docs/core/extensions/dependency-injection.md

@@ -3,7 +3,7 @@ title: Dependency injection in .NET
 description: Learn how .NET implements dependency injection and how to use it.
 author: IEvangelist
 ms.author: dapine
-ms.date: 09/23/2020
+ms.date: 10/28/2020
 ms.topic: overview
 ---
 
@@ -205,16 +205,41 @@ The framework provides service registration extension methods that are useful in
 
 For more information on type disposal, see the [Disposal of services](dependency-injection-guidelines.md#disposal-of-services) section.
 
+Registering a service with only an implementation type is equivalent to registering that service with the same implementation and service type. This is why multiple implementations of a service cannot be registered using the methods that don't take an explicit service type. These methods can register multiple *instances* of a service, but they will all have the same *implementation* type.
+
+Any of the above service registration methods can be used to register multiple service instances of the same service type. In the following example, `AddSingleton` is called twice with `IMessageWriter` as the service type. The second call to `AddSingleton` overrides the previous one when resolved as `IMessageWriter` and adds to the previous one when multiple services are resolved via `IEnumerable<IMessageWriter>`. Services appear in the order they were registered when resolved via `IEnumerable<{SERVICE}>`.
+
+:::code language="csharp" source="snippets/configuration/console-di-ienumerable/Program.cs" highlight="19-24":::
+
+The preceding sample source code registers two implementations of the `IMessageWriter`.
+
+:::code language="csharp" source="snippets/configuration/console-di-ienumerable/ExampleService.cs" highlight="9-18":::
+
+The `ExampleService` defines two constructor parameters; a single `IMessageWriter`, and an `IEnumerable<IMessageWriter>`. The single `IMessageWriter` is the last implemenation to have been registered, whereas the `IEnumerable<IMessageWriter>` represents all registered implementations.
+
 The framework also provides `TryAdd{LIFETIME}` extension methods, which register the service only if there isn't already an implementation registered.
 
-In the following example, the call to `AddSingleton` registers `MessageWriter` as an implementation for `IMessageWriter`. The call to `TryAddSingleton` has no effect because `IMessageWriter` already has a registered implementation:
+In the following example, the call to `AddSingleton` registers `ConsoleMessageWriter` as an implementation for `IMessageWriter`. The call to `TryAddSingleton` has no effect because `IMessageWriter` already has a registered implementation:
 
 ```csharp
-services.AddSingleton<IMessageWriter, MessageWriter>();
-services.TryAddSingleton<IMessageWriter, DifferentMessageWriter>();
+services.AddSingleton<IMessageWriter, ConsoleMessageWriter>();
+services.TryAddSingleton<IMessageWriter, LoggingMessageWriter>();
 ```
 
-The `TryAddSingleton` has no effect, as it was already added and the "try" will fail.
+The `TryAddSingleton` has no effect, as it was already added and the "try" will fail. The `ExampleService` would assert the following:
+
+```csharp
+public class ExampleService
+{
+    public ExampleService(
+        IMessageWriter messageWriter,
+        IEnumerable<IMessageWriter> messageWriters)
+    {
+        Trace.Assert(messageWriter is ConsoleMessageWriter);
+        Trace.Assert(messageWriters.Single() is ConsoleMessageWriter);
+    }
+}
+```
 
 For more information, see:
 

docs/core/extensions/snippets/configuration/app-lifetime/app-lifetime.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-custom-logging/console-custom-logging.csproj

@@ -7,8 +7,8 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
-    <PackageReference Include="Microsoft.Extensions.Logging" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
+    <PackageReference Include="Microsoft.Extensions.Logging" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-di-disposable/console-di-disposable.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-di-ienumerable/ConsoleMessageWriter.cs

@@ -0,0 +1,11 @@
+using System;
+
+namespace ConsoleDI.IEnumerableExample
+{
+    public class ConsoleMessageWriter : IMessageWriter
+    {
+        public void Write(string message) => 
+            Console.WriteLine(
+                $"ConsoleMessageWriter.Write(message: \"{message}\")");
+    }
+}

docs/core/extensions/snippets/configuration/console-di-ienumerable/ExampleService.cs

@@ -0,0 +1,20 @@
+using System.Collections.Generic;
+using System.Diagnostics;
+using System.Linq;
+
+namespace ConsoleDI.IEnumerableExample
+{
+    public class ExampleService
+    {
+        public ExampleService(
+            IMessageWriter messageWriter,
+            IEnumerable<IMessageWriter> messageWriters)
+        {
+            Trace.Assert(messageWriter is LoggingMessageWriter);
+
+            var dependencyArray = messageWriters.ToArray();
+            Trace.Assert(dependencyArray[0] is ConsoleMessageWriter);
+            Trace.Assert(dependencyArray[1] is LoggingMessageWriter);
+        }
+    }
+}

docs/core/extensions/snippets/configuration/console-di-ienumerable/IMessageWriter.cs

@@ -0,0 +1,7 @@
+namespace ConsoleDI.IEnumerableExample
+{
+    public interface IMessageWriter
+    {
+        void Write(string message);
+    }
+}

docs/core/extensions/snippets/configuration/console-di-ienumerable/LoggingMessageWriter.cs

@@ -0,0 +1,15 @@
+using Microsoft.Extensions.Logging;
+
+namespace ConsoleDI.IEnumerableExample
+{
+    public class LoggingMessageWriter : IMessageWriter
+    {
+        private readonly ILogger<LoggingMessageWriter> _logger;
+
+        public LoggingMessageWriter(ILogger<LoggingMessageWriter> logger) =>
+            _logger = logger;
+
+        public void Write(string message) =>
+            _logger.LogInformation(message);
+    }
+}

docs/core/extensions/snippets/configuration/console-di-ienumerable/Program.cs

@@ -0,0 +1,26 @@
+using System.Threading.Tasks;
+using ConsoleDI.IEnumerableExample;
+using Microsoft.Extensions.DependencyInjection;
+using Microsoft.Extensions.Hosting;
+
+namespace ConsoleDI.Example
+{
+    class Program
+    {
+        static Task Main(string[] args)
+        {
+            IHost host = CreateHostBuilder(args).Build();
+
+            _ = host.Services.GetService<ExampleService>();
+
+            return host.RunAsync();
+        }
+
+        static IHostBuilder CreateHostBuilder(string[] args) =>
+            Host.CreateDefaultBuilder(args)
+                .ConfigureServices((_, services) =>
+                    services.AddSingleton<IMessageWriter, ConsoleMessageWriter>()
+                            .AddSingleton<IMessageWriter, LoggingMessageWriter>()
+                            .AddSingleton<ExampleService>());
+    }
+}

docs/core/extensions/snippets/configuration/console-di-ienumerable/console-di-ienumerable.csproj

@@ -0,0 +1,13 @@
+<Project Sdk="Microsoft.NET.Sdk">
+
+  <PropertyGroup>
+    <OutputType>Exe</OutputType>
+    <TargetFramework>net5.0</TargetFramework>
+    <RootNamespace>ConsoleDI.IEnumerableExample</RootNamespace>
+  </PropertyGroup>
+
+  <ItemGroup>
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
+  </ItemGroup>
+
+</Project>

docs/core/extensions/snippets/configuration/console-di/console-di.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-env/console-env.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-host/console-host.csproj

@@ -17,8 +17,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0-rc.1.20451.14" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0-rc.2.20475.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-ini/console-ini.csproj

@@ -17,8 +17,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Configuration.Ini" Version="5.0.0-rc.1.20451.14" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Ini" Version="5.0.0-rc.2.20475.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-json/console-json.csproj

@@ -17,8 +17,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0-rc.1.20451.14" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Json" Version="5.0.0-rc.2.20475.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-memory/console-memory.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console-xml/console-xml.csproj

@@ -21,8 +21,8 @@
   </ItemGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Configuration.Xml" Version="5.0.0-rc.1.20451.14" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Configuration.Xml" Version="5.0.0-rc.2.20475.5" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/console/console.csproj

@@ -7,7 +7,7 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/custom-provider/custom-provider.csproj

@@ -7,9 +7,9 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="5.0.0-rc.1.20451.13" />
-    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="5.0.0-rc.1.20451.13" />
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore" Version="5.0.0-rc.2.20475.6" />
+    <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="5.0.0-rc.2.20475.6" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 
 </Project>

docs/core/extensions/snippets/configuration/dependency-injection/LoggingMessageWriter.cs

@@ -9,7 +9,7 @@ public class LoggingMessageWriter : IMessageWriter
         public LoggingMessageWriter(ILogger<LoggingMessageWriter> logger) =>
             _logger = logger;
 
-        public void Write(string message) => 
+        public void Write(string message) =>
             _logger.LogInformation(message);
     }
 }

docs/core/extensions/snippets/configuration/dependency-injection/dependency-injection.csproj

@@ -6,6 +6,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 </Project>

docs/core/extensions/snippets/configuration/worker-service-options/worker-service-options.csproj

@@ -8,6 +8,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 </Project>

docs/core/extensions/snippets/configuration/worker-service/worker-service.csproj

@@ -7,6 +7,6 @@
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.1.20451.14" />
+    <PackageReference Include="Microsoft.Extensions.Hosting" Version="5.0.0-rc.2.20475.5" />
   </ItemGroup>
 </Project>