C# namespace alias - what's the point?

Question

I have been trying to learn more about the C# language, but I haven't been able to see a situation where one would use namespace aliasing like

 using someOtherName =  System.Timers.Timer;

It seems to me that it would just add more confusion to understanding the language. Could some one please explain.

Thanks

Answer 1

That is a type alias, not a namespace alias; it is useful to disambiguate - for example, against:

using WinformTimer = System.Windows.Forms.Timer;
using ThreadingTimer = System.Threading.Timer;

(ps: thanks for the choice of Timer ;-p)

Otherwise, if you use both System.Windows.Forms.Timer and System.Timers.Timer in the same file you'd have to keep giving the full names (since Timer could be confusing).

It also plays a part with extern aliases for using types with the same fully-qualified type name from different assemblies - rare, but useful to be supported.

---

Actually, I can see another use: when you want quick access to a type, but don't want to use a regular using because you can't import some conflicting extension methods... a bit convoluted, but... here's an example...

namespace RealCode {
    //using Foo; // can't use this - it breaks DoSomething
    using Handy = Foo.Handy;
    using Bar;
    static class Program {
        static void Main() {
            Handy h = new Handy(); // prove available
            string test = "abc";            
            test.DoSomething(); // prove available
        }
    }
}
namespace Foo {
    static class TypeOne {
        public static void DoSomething(this string value) { }
    }
    class Handy {}
}
namespace Bar {
    static class TypeTwo {
        public static void DoSomething(this string value) { }
    }
}

Answer 2

It is very useful when you have multiple classes with the same name in multiple included namespaces. For example...

namespace Something.From.SomeCompanyA {
    public class Foo {
        /* ... */
    }
}

namespace CompanyB.Makes.ThisOne {
    public class Foo {
        /* ... */
    }
}

You can use aliases to make the compiler happy and to make things more clear for you and others on your team:

using CompanyA = Something.From.CompanyA;
using CompanyB = CompanyB.Makes.ThisOne;

/* ... */

CompanyA.Foo f = new CompanyA.Foo();
CompanyB.Foo x = new CompanyB.Foo();

Answer 3

I always use it in situations like this

using Utility = MyBaseNamespace.MySubNamsepace.Utility;

where Utility would otherwise have a different context (like MyBaseNamespace.MySubNamespace.MySubSubNamespace.Utility), but I expect/prefer Utility to always point to that one particular class.

Answer 4

Brevity.

There are fringe benefits to provide clarity between namespaces which share type names, but essentially it's just sugar.

Answer 5

I use it when I've got multiple namespaces with conflicting sub namespaces and/or object names you could just do something like [as an example]:

using src = Namespace1.Subspace.DataAccessObjects;
using dst = Namespace2.Subspace.DataAccessObjects;

...

src.DataObject source = new src.DataObject();
dst.DataObject destination = new dst.DataObject();

Which would otherwise have to be written:

Namespace1.Subspace.DataAccessObjects.DataObject source = 
  new Namespace1.Subspace.DataAccessObjects.DataObject();

Namespace2.Subspace.DataAccessObjects.DataObject dstination = 
  new Namespace2.Subspace.DataAccessObjects.DataObject();

It saves a ton of typing and can be used to make code a lot easier to read.

Answer 6

We have defined namespace aliases for all of our namespaces. This makes it very easy to see where a class comes from, e.g:

using System.Web.WebControls;
// lots of other using statements

// contains the domain model for project X
using dom = Company.ProjectX.DomainModel; 
// contains common web functionality
using web = Company.Web;
// etc.

and

// User from the domain model
dom.User user = new dom.User(); 
// Data transfer object
dto.User user = new dto.User(); 
// a global helper class
utl.SomeHelper.StaticMethod(); 
// a hyperlink with custom functionality
// (as opposed to System.Web.Controls.HyperLink)
web.HyperLink link = new web.HyperLink();

We have defined some guidelines how the aliases must be named and everyone is using them.

Answer 7

In addition to the examples mentioned, type aliases (rather than namespace aliases) can be handy when repeatedly referring to generic types:

Dictionary<string, SomeClassWithALongName> foo = new Dictionary<string, SomeClassWithALongName>();

private void DoStuff(Dictionary<string, SomeClassWithALongName> dict) {}

Versus:

using FooDict = Dictionary<string, SomeClassWithALongName>;

FooDict foo = new FooDict();

private void DoStuff(FooDict dict) {}