Oleg Sych

Here is how MSDN documentation defines the import directive.

By using the import directive, you can refer to types in a text template without providing a fully qualified name.

Here is what happens under the hood.

Template

<#@ template language="C#" debug="True" #>
<#@ import namespace="System.Diagnostics" #>
<#
    Debugger.Break();
#>

Compiled Template

using System;
using System.Diagnostics;
using Microsoft.VisualStudio.TextTemplating;  

namespace Microsoft.VisualStudio.TextTemplating559506E3E78F9B3E7
{
    public class GeneratedTextTransformation: TextTransformation
    {
        public override string TransformText()
        {
            Debugger.Break();
            return this.GenerationEnvironment.ToString();
        }
    }
}

Notice that T4 transformed the import directive into a C# using directive in the compiled template. That allowed us to reference System.Diagnostics.Debugger class in the template code without specifying its namespace.

About T4

T4 (Text Template Transformation Toolkit) is a template-based code generation engine. It is available in Visual Studio 2008 and as a download in DSL and GAT toolkits for Visual Studio 2005. T4 engine allows you to use ASP.NET-like template syntax to generate C#, T-SQL, XML or any other text files.

Ready for more? Read about <#@ assembly #> directive or go back to the overview.