How expensive is a DLL reference?

Question

Either local or global (GAC / .NET) DLL references, how expensive they are?

For sure we should never reference things we don't use, but for curiosity I ask: Would it be a big performance concern referencing the whole .NET framework?

A similar more practical question would be: Is it worth to combine similar namespaces in projects to minimize the DLL files that need to be referenced (as long as I have to use every code in those DLLs in any case)?

Answer 1

A reference is loaded only when you execute a method, which uses a type from the referenced .dll. So even if you reference the whole .NET framework, it will not be loaded automatically.

class Program
{
    static void Main(string[] args)
    {
        AppDomain.CurrentDomain.AssemblyLoad += CurrentDomain_AssemblyLoad;
        Console.WriteLine("=====Working with URI...=====");
        WorkWithUri();

        Console.WriteLine("=====Working with XML...=====");
        WorkWithXml();
    }

    private static void CurrentDomain_AssemblyLoad(object sender, AssemblyLoadEventArgs args)
    {
        Console.WriteLine(args.LoadedAssembly.FullName + " has been loaded.");
    }

    private static void WorkWithUri()
    {
        var uri = new Uri("c:\\");
    }

    private static void WorkWithXml()
    {
        XDocument xml = new XDocument();
    }
}

And the output:

=====Working with URI...=====
System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 has been loaded.
=====Working with XML...=====
System.Xml.Linq, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 has been loaded.
System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 has been loaded.
System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 has been loaded.
Press any key to continue . . .