Using directives often contain a repeated subset across all the files in a project.

Global using directives allow you to exclude this common boilerplate across your project.

In conjunction with implicit usings (see notes below) using directives can be hidden entirely.

Code

Now

// In GlobalUsings.cs file
global using System;
global using System.Collections.Generic;
global using System.Linq;

// In EmployeeRepository.cs file
public class EmployeeRepository : Repository {
    public List<Employee> GetByDepartment(int departmentId) {
        return db.Employees.Where(e => e.DepartmentId == departmentId).ToList();
    }
}

Before

using System;
using System.Collections.Generic;
using System.Linq;

public class EmployeeRepository : Repository {
    public List<Employee> GetByDepartment(int departmentId) {
        return db.Employees.Where(e => e.DepartmentId == departmentId).ToList();
    }
}

Notes

• Consider putting global using directives in a single shared obvious file like GlobalUsings.cs although this isn't required
• global using directives must come before any non-global using directives in a file, and also work with static and aliases
• You can enable implicit usings (.NET 6 SDK onwards) by adding <ImplicitUsings>enable</ImplicitUsings> to a <PropertyGroup> in your .csproj file or selecting Enable implicit global usings to be declared by the project SDK in the Visual Studio project settings UI
• This is great for unit test projects where you can add global using Xunit; to your GlobalUsings.cs file and then use Fact and Theory without any additional using directives

More information

• Specification
• C# Reference
• Implicit global using directives @endjin