VB.NET namespace abbreviation: How do I make this work in equivalent C# code?

Question

I am a VB.NET programmer by nature and I am having a hard time figuring this out. Any help with the following would be appreciated.

I need to get the C# code (1) below to work. The VB.NET equivalent works just fine, but the C# does not.

Note that both (2) and (3) do work, but this is actually auto-generated code, and I need the VB.NET and C# versions to be as similar as possible.

1. This does not compile (the fully-qualified name of Engine is ThreeD.QVB.Engine):

   using ThreeD.QVB;
   
   namespace QVBScript
   {
       public class ScriptCode
       {
           public void Main(ref Engine.QVBObjectsDictionary objects,
                            Engine.Commands commands)
           {
               …
   

2. However, this does work:

   //using ThreeD.QVB; // I'm instead using fully-qualified names in the method
   
   namespace QVBScript
   {
       public class ScriptCode
       {
           public void Main(ref ThreeD.QVB.Engine.QVBObjectsDictionary objects,
                           ThreeD.QVB.Engine.Commands commands)
           {
               …
   

3. This works, too:

   using eng = ThreeD.QVB.Engine;
   
   namespace QVBScript
   {
       public class ScriptCode
       {
           public void Main(ref eng.QVBObjectsDictionary objects, 
                            eng.Commands commands)
           {
               …
   

Answer 1

In VB.NET if you have an import for the first part of a namespace, you can reference just the later half. In C# you cannot do this. You must have a using for the full namespace, or fully qualify your type names. Different languages, different rules.

In your last example you do not need to use the alias.

using ThreeD.QVB.Engine;

namespace QVBScript
{
    public class ScriptCode
    {
        public void Main(ref QVBObjectsDictionary objects, Commands commands)
        {
            UI.Output Output = (UI.Output)objects["Output"];

Answer 2

Basic rules to remember:

using A.B;

• does allow you to refer to types from namespaces A and A.B without fully qualifying them with their namespace (everywhere in the same file).

• does not allow you to abbreviate the names of sub-namespaces of A or A.B. by omitting the A. or A.B. part from their names.

namespace A.B { … }

• does allow you to refer to types from namespaces A and A.B without fully qualifying them with their namespace (inside the block).

• does allow you to abbreviate the names of sub-namespaces of A or A.B by omitting the A. or A.B. part from their names.

---

Example:

using System.Collections;

namespace A
{
  class Top : IDisposable, // importing System.Collections also imports System   
              IEnumerable, // inside the imported namespace
              System.Collections.Generic.IEnumerable<int>
  {…}                      // ^ "using" does not permit namespace abbreviation
}

namespace A.B
{
  class Middle : Top,      // namespace A available inside namespace A.B
                 C.IBottom // namespace blocks permit namespace abbreviation
  {…}
}

namespace A.B.C
{
  interface IBottom {…}
}