Namespace Alias Qualifier

Technorati Tags: C#,Namespace,Alias,Qualifier,Global,Attribute,Auto-generator,Code Generator

 

I have noticed a trend with code auto-generated from Microsoft tools.

 

Here is a sample section of code as I would have viewed it in older samples:

Code Snippet

   23     [System.Data.Objects.DataClasses.EdmEntityTypeAttribute(NamespaceName = "PizzaModel", Name = "PizzaOrder")]

   24     [System.Runtime.Serialization.DataContractAttribute()]

   25     [System.Serializable()]

   26     public partial class PizzaOrder : System.Data.Objects.DataClasses.EntityObject {

 

This is the exact same code, except it includes the more recent changes that I happened to notice:

Code Snippet

   23     [global::System.Data.Objects.DataClasses.EdmEntityTypeAttribute(NamespaceName = "PizzaModel", Name = "PizzaOrder")]

   24     [global::System.Runtime.Serialization.DataContractAttribute()]

   25     [global::System.Serializable()]

   26     public partial class PizzaOrder : global::System.Data.Objects.DataClasses.EntityObject {

 

Notice the reference to 'global::'? Apparently, Visual Studio and ultimately the compiler can potentially be confused.

 

Here is a link to the Namespace Alias Qualifier:

http://msdn2.microsoft.com/en-us/library/c3ay4x3d(VS.80).aspx

 

According to that sample, you may have a namespace TestApp and within that TestApp namespace have a constant named Console within a class named System. The example also shows a using statement referencing the namespace System. That combination is apparently deadly to the compiler and even though Console.WriteLine() exists within the System namespace; it cannot be referenced because it conflicts with the Console constant. Here is the "non-working" code:

Code Snippet

    1 using System;

    // yada yada ...

    8     class TestApp {

    9         // Define a new class called 'System' to cause problems.

   10         public class System { }

   11 

   12         // Define a constant called 'Console' to cause more problems.

   13         const int Console = 7;

   14         const int number = 66;

   15 

   16         static void Main() {

   17             // Error  Accesses TestApp.Console

   18             //Console.WriteLine(number);

   19         }

   20     }

 

To the rescue: We have the 'global::' namespace qualifier available which forces a namespace comparison to be  based on the entire namespace starting from the root. I can only assume that namespace collisions (at least for Microsoft) happen more often than we assume; especially, when code generators are involved.

It is one thing to create and compile code within Visual Studio, but its entirely different if you are creating/ managing a code generator where you can never be sure of namespace conflicts. I happen to use CodeDOM (http://msdn2.microsoft.com/en-us/library/y2k85ax6.aspx) and understand completely how this could benefit my auto-generated code.

If you auto-generate code, it may be wise to to include a global reference similar to the new trend I am noticing. If you do not, this post may be helpful to simply understand the global reference.