Global using Directive in C# 10

The "global using" directive in C# 10 is a new feature that simplifies the inclusion of commonly used namespaces across the entire codebase of a C# project. It allows you to declare using directives at the project level, eliminating the need to include them in individual source code files.

Traditional Using Directives

In C# projects prior to version 10, you needed to include using directives at the top of each source code file where you wanted to use specific namespaces.

using System; using System.Collections.Generic; using System.Linq; using System.Threading.Tasks; namespace MyNamespace { // ... }

Global Using Directive in C# 10

To use the global using directive, you simply add the global keyword to the using directive. For example, the following code imports the System namespace at the global level:

global using System;

Once you have imported a namespace at the global level, you can use the types in that namespace without having to qualify them with the namespace name. For example, the following code uses the Console class from the System namespace without having to qualify it with the System namespace name:

Console.WriteLine("Hello, world!");

You can use the global using directive to import any namespace, including namespaces that you have defined yourself. This can be useful for organizing your code and making it more reusable.

With C# 10's "global using" directive, you can move these using directives to a central location, typically in a file named GlobalUsings.cs, at the project level.

This simplifies the management of using directives and reduces the need to repeat them in every source code.

GlobalUsings.cs
global using System; global using System.Collections.Generic; global using System.Linq; global using System.Threading.Tasks;

Using the Global Using Directive

Once you've defined the global using directives in GlobalUsings.cs, you can access those namespaces in any source code file within the same project without explicitly including them.

namespace MyNamespace { class Program { static void Main() { List<int> numbers = new List<int> { 1, 2, 3 }; var sum = numbers.Sum(); // No need for 'using System.Linq;' Console.WriteLine(sum); } } }

In this example, the using System.Linq; directive is not required in the source code file because it's included globally through the "global using" directive.

Benefits of Global Using Directives

  1. Reduced boilerplate code: The global using directive can help to reduce the amount of boilerplate code in your program, especially if you are using a lot of different namespaces.
  2. Improved code readability: The global using directive can make your code more readable by making it easier to see which namespaces are being used.
  3. Improved code maintainability: The global using directive can make your code more maintainable by making it easier to change the namespaces that are being used without affecting the rest of the code.

However, it is important to use the global using directive carefully, as it can make your code less readable and maintainable if it is used excessively. For example, if you import too many namespaces at the global level, it can be difficult to keep track of which types are being used from which namespaces.

Considerations

  1. While "global using" directives are convenient, you should use them judiciously to avoid polluting the global namespace with unnecessary imports.
  2. They are typically used for namespaces that are commonly used across many parts of the project, like System, System.Linq, or project-specific namespaces.

Conclusion

The "global using" directive in C# 10 allows developers to declare common using directives at the project level, eliminating the need to repeat them in every source code file. This simplifies code maintenance, enhances consistency, and promotes efficient namespace management across the entire project, making it a valuable feature for improving code organization in C# projects.