Stylistic differences in using
There are two ways in which you can use using directive as outlined below
Style 1
using
System;using
System.Collections.Generic;using
System.Text;namespace
MyNameSpace{
// ...
}
Style 2
namespace
MyNameSpace{
using System;
using System.Collections.Generic;
using System.Text;
// ...
}
With respect to scoping both the styles have the same effect on all the code inside the MyNameSpace.
Microsoft tools seem to differ in which style is preferred. Style-1 is used by the source template in the CSharp projects, so if you create a new project the files generated will use the first style. However, in case you use CodeDom to generate code in C#, it uses the second style (note in VB.NET it uses the first style).
Stylecop also fails the first style with the note that Using directives must be inside of a namespace element.
I am using CodeDom to generate some code and I tried to figure out the benefits of the 2nd style as the code is generated in that format. I found out the following benefits
- Lowers the chances of namespace pollution in case the source file has more than one namespace declaration in it
- Reduces the size of the drop down in intellisense
- Conflict detection in aliasing
Jay Thaler pointed me out the last one. The example goes as follows
using
System;using
Uri = System.Uri;namespace
MyNamespace{
public class MyClass
{
public void DoIt()
{
new Uri();
}
}
public class Uri
{
}
}
In this code the class Uri will silently override the Uri alias. However, compilation of the following will fail with error CS0576: Namespace 'MyNamespace' contains a definition conflicting with alias 'Uri'
namespace
MyNamespace{
using System;
using
Uri = System.Uri; public class MyClass
{
public void DoIt()
{
new Uri();
}
}
public class Uri
{
}
}
