Scott Hanselman

Implicit Usings in .NET 6

September 16, 2021 Comment on this post [2] Posted in DotNetCore
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Magic".NET 6 introduces implicit namespace support for C# projects. To reduce the amount of using directives boilerplate in .NET C# project templates, namespaces are implicitly included by utilizing the global using feature introduced in C# 10."

NOTE: Did you know that Visual Basic has had this very feature forever?

Remember that C# as a language is itself versioned and in .NET 6 we'll have support for C# 10 features like global usings, which are super cool.

Since we don't want to break existing stuff, there's some things to consider. First, for new projects this is on by default but for existing projects this will be off by default. This offers the best of both worlds.

When you create a new .NET 6 project it will enable this new property:

<ImplicitUsings>enable</ImplicitUsings>

Read more about this breaking change here. This build property builds upon (utilizes) the C# global using feature feature which means any .cs in your project can have a line like:

global using global::SomeNamespace;

The SDK uses a target to autogenerate a .cs file called ImplicitNamespaceImports.cs that will be in your obj folder, but you can - if you desire - have full control and add or remove namespaces to taste.

This gives advanced users who understand target file a huge amount control while still allowing newbies to reap the benefits. Other way to think about it is - if you care, you can control it all. If you don't, it'll just make things easier and cleaner.

Let's look at some code to point out that it's pretty cool. Oleg gives a great example doing some basic threading where there's three lines of code (cool) and three more lines of usings to bring in the namespace support for the actual work (less cool).

using System;
using System.Collections.Generic;
using System.Threading.Tasks;

Console.WriteLine("Hello World");
await Task.Delay(1000);
List<int> _ = new ();

With implicating usings (implicitly bringing in default namespaces) .NET apps with C# 10 can do more out of the box. It's faster to get started because the 90% of the stuff you do all the time is already available and ready to be used!

Maybe this example is too simple? What If you were using a simple Web Worker app? Check out Wade's example.

System
System.Collections.Generic
System.IO
System.Linq
System.Net.Http
System.Threading
System.Threading.Tasks
System.Net.Http.Json
Microsoft.AspNetCore.Builder
Microsoft.AspNetCore.Hosting
Microsoft.AspNetCore.Http
Microsoft.AspNetCore.Routing
Microsoft.Extensions.Configuration
Microsoft.Extensions.DependencyInjection
Microsoft.Extensions.Hosting
Microsoft.Extensions.Logging
Microsoft.Extensions.Configuration
Microsoft.Extensions.DependencyInjection
Microsoft.Extensions.Hosting
Microsoft.Extensions.Logging

This is a lot of boilerplate if you just want a web app. If I'm using the Microsoft.Net.Sdk.Worker SDK in my project file, or just Microsoft.NET.Sdk.Web, I don't have think about or include any of these - they are there implicitly!

You may initially love implicit usings, as I do, or you may find it to be too "magical." I would remind you that most innovations feel magical, especially if they aren't in your face. The Garbage Collector is taken for granted by the majority of .NET developers, while I found it magical when I had spent the previous 10 years managing my own memory down to the byte.

Hope you enjoy this new feature as we get closer to .NET 6's release.


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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September 25, 2021 8:22
Hmmmmmmmm sounds great.
Now, who is going to write a refactoring shortcut to move usings to global?
A second thing that comes to mind is if a class exists in more than one global namespace, how do you ensure that you are using the exact one you want?
September 25, 2021 12:44
@James, the

using SomeClass = MyOwnNamespace.SomeClass;

method still work in case you have a conflict

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.