You can export your .NET class for use with existing COM components, although this is an unusual requirement. The Regasm tool will register the metadata from your component in the system registry.

You invoke Regasm with the name of the DLL. For example:

Regasm myAssembly.dll

This will export your component’s metadata to the Registry. For example, you can create a new C# DLL project in which you re-create your four-function calculator, as shown in Example 22-8.

using System;

namespace Programming_CSharp
{
    public class Calculator
    {
        public Calculator(  )
        {
            
        }
        public Double Add (Double left, Double right)
        {
            return left + right;
        }
        public Double Subtract (Double left, Double right)
        {
            return left - right;
        }
        public Double Multiply (Double left, Double right)
        {
            return left * right;
        }
        public Double Divide (Double left, Double right)
        {
            return left / right;
        }
    }
}

You save this to a file named Calculator.cs in a project named ProgrammingCSharpDLL. After building this project, you can register it with:

Regasm ProgrammingCSharpDLL.dll

A quick check of the Registry shows that a PROGID was created for the DLL, as shown in Figure 22-18.

Figure 22-18. The Registry after registering the DLL

You can now invoke the four-function calculator as a COM object using standard VBScript. For example, you can create a tiny Windows Script Host file, as shown in Example 22-9.

dim calc
dim msg 
dim result 
set calc = CreateObject("ProgrammingCSharpDLL.Calculator") 
result = calc.Multiply(7,3) 
msg = "7 * 3 =" & result & "."
Call MsgBox(msg)

When this is run, a dialog box pops up to verify that the object was created and invoked, as shown in Figure 22-19.

Figure 22-19. Late binding via COM

Creating a Type Library

If you wish to use early binding with your .NET DLL you will need to create a type library. You can do so with the TlbExp (Type Library Export) utility, by writing:

TlbExp ProgrammingCSharpDLL.dll /out:Calc.tlb

The result is a type lib that you can browse for and view in the OLE/COM object viewer within Visual Studio, as shown in Figure 22-20.

Figure 22-20. Viewing the type lib contents

With this type library in hand, you can import the calculator class into any COM environment.