2020-10-25-Options-DavidF

OptionsGist.csproj

<Project Sdk="Microsoft.NET.Sdk">

  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net5.0</TargetFramework>
    <LangVersion>preview</LangVersion>
  </PropertyGroup>

  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.DependencyInjection" Version="5.0.0-rc.2.20475.5" />
    <PackageReference Include="Microsoft.Extensions.Options" Version="5.0.0-rc.2.20475.5" />
    <PackageReference Include="Xunit" Version="2.4.1" />
  </ItemGroup>

</Project>

Program.cs

//
// To run: `dotnet run` (should display `All Good!`)
// Requires .NET 5 SDK
// Uses C# 9 preview features
//
using System;
using Microsoft.Extensions.DependencyInjection;
using Microsoft.Extensions.Options;
using Xunit;

var services = new ServiceCollection();

// Configure MyOptions and consumers
services.Configure<MyOptions>(x => new MyOptions { Name = "Whatever" });
services.Configure<MyOptions>("MagicName", x => new MyOptions { Name = "MagicName" });
services.AddTransient<MeControlOptionsLifetimeSingleton>();
services.AddTransient<MeControlOptionsLifetimeScoped>();
services.AddTransient<MeDontControlOptionsLifetime>();
services.AddTransient<MeControlOptionName>();

// This is an example of how to bind MyOptions to an "IOptionsWhatever<T>"
// This could be anything that would make sense for any given concrete scenario
services.AddTransient<MyOptions>(sp => sp.GetRequiredService<IOptionsMonitor<MyOptions>>().CurrentValue);

// Using the registered stuff just for fun :)
var serviceProvider = services.BuildServiceProvider();
var meControlOptionsLifetimeSingleton = serviceProvider.GetRequiredService<MeControlOptionsLifetimeSingleton>();
var meControlOptionsLifetimeScoped = serviceProvider.GetRequiredService<MeControlOptionsLifetimeScoped>();
var meDontControlOptionsLifetime = serviceProvider.GetRequiredService<MeDontControlOptionsLifetime>();
var meControlOptionName = serviceProvider.GetRequiredService<MeControlOptionName>();

// Making sure that all is rigged correctly (while at it)
Assert.Same(meControlOptionsLifetimeSingleton.Options.CurrentValue, meDontControlOptionsLifetime.Options);
Assert.NotSame(meControlOptionsLifetimeSingleton.Options.CurrentValue, meControlOptionsLifetimeScoped.Options.Value);
Assert.NotSame(meControlOptionName.Options, meControlOptionsLifetimeSingleton.Options.CurrentValue);
Console.WriteLine("All Good!");

// Some options
public class MyOptions
{
    public string Name { get; set; }
}

// This class controls the lifetime of its MyOptions dependency. 
// By injecting a IOptionsMonitor<T>, MeControlOptionsLifetimeSingleton decides that it wants a singleton lifetime.
// To change the lifetime of that MyOptions, we must update MeControlOptionsLifetimeSingleton
// Not IoC
public record MeControlOptionsLifetimeSingleton(IOptionsMonitor<MyOptions> Options);

// This class controls the lifetime of its MyOptions dependency. 
// By injecting a IOptionsSnapshot<T>, MeControlOptionsLifetimeScoped decides that it wants a scoped lifetime.
// To change the lifetime of that MyOptions, we must update MeControlOptionsLifetimeScoped
// Not IoC
public record MeControlOptionsLifetimeScoped(IOptionsSnapshot<MyOptions> Options);

// This class don't control the lifetime of its MyOptions dependency.
// By injecting MyOptions directly, MeDontControlOptionsLifetime lets the composition root manage the MyOptions's lifetime.
// To change the lifetime of that MyOptions, we must update the composition root (a good thing)
// Yes: IoC
public record MeDontControlOptionsLifetime(MyOptions Options);

// This class controls the lifetime of its MyOptions dependency. 
// This class controls what instance of MyOptions is "created" (by name).
// To change the lifetime of that MyOptions, we must update MeControlOptionName
// To change the created instance of MyOptions, we must update MeControlOptionName (change "MagicName" by something else)
// Not IoC
public class MeControlOptionName
{
    public MyOptions Options { get; }
    public MeControlOptionName(IOptionsFactory<MyOptions> factory)
    {
        Options = factory.Create("MagicName");
    }
}