What’s New in C# 10: Write Less Code and Reduce Repeated Using Directives

This is part of a series on the new features introduced with C# 10.

There are 2 related features in C# 10 that will reduce the clutter of repetitive using directives: global using directives and implicit global using directives.

C# 10 Global Usings

At the top of every code file you will usually find a number of using directives:

using ConsoleApp1.Configuration;

namespace ConsoleApp1
{
    internal class Calculator
    {
        public int Add(int a, int b)
        {
            if (CalculatorConfiguration.SomeConfigProperty)
            {
                // etc.
            }
            return a + b;
        }
    }
}

In the preceding code there is a single using ConsoleApp1.Configuration; to get access to a CalculatorConfiguration class.

For one file this is not much overhead in terms of repeated code.

Imagine however if the CalculatorConfiguration class was referenced in 100’s of code files throughout the project. This would mean we’d have 100 using ConsoleApp1.Configuration; lines throughout the project.

As an alternative you can use the new global using declarations. To use these just prefix the directive with global, for example: global using ConsoleApp1.Configuration;

Now all code files in the project will act as if though they have a using ConsoleApp1.Configuration; at the top of them. You only need one global using directive for any given namespace in the project.

You can add global usings to any code file, however it makes sense to centralize them. For example you could create a GlobalUsings.cs file in the project and inside that just have all your global using directives.

C# 10 Implicit Global Usings

If you create a new C# 10 project (e.g. a console app) and open the project file you’ll see a line: <ImplicitUsings>enable</ImplicitUsings>

This enables the new implicit global usings feature.

When this feature is enabled, a number of commonly used namespaces will automatically have global usings directives added for them.

For a Console project the following will be automatically added:

// 
global using global::System;
global using global::System.Collections.Generic;
global using global::System.IO;
global using global::System.Linq;
global using global::System.Net.Http;
global using global::System.Threading;
global using global::System.Threading.Tasks;

This means for example you you could create a List<string> anywhere in the project without needing to add a using System.Collections.Generic; to the top of your code files.

Implicit global usings work behind the scenes by generating a file.

Assuming you had a console app called ConsoleApp1, you would find this generated file as follows: "ConsoleApp1\obj\Debug\net6.0\ConsoleApp1.GlobalUsings.g.cs".

If you opened this file you’d see the global usings that are implicitly added to your project.

If you don’t like the idea of implicit global usings you can opt out for new projects by making the following change in the project file: <ImplicitUsings>disable</ImplicitUsings>

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