How do I alias a class name in C#, without having to add a line of code to every file that uses the class?

Question

i want to create an alias for a class name. The following syntax would be perfect:

public class LongClassNameOrOneThatContainsVersionsOrDomainSpecificName
{
   ...
}

public class MyName = LongClassNameOrOneThatContainsVersionOrDomainSpecificName;

but it won't compile.

---

Example

Note This example is provided for convience only. Don't try to solve this particular problem by suggesting changing the design of the entire system. The presence, or lack, of this example doesn't change the original question.

Some existing code depends on the presence of a static class:

public static class ColorScheme
{
   ...
}

This color scheme is the Outlook 2003 color scheme. i want to introduce an Outlook 2007 color scheme, while retaining the Outlook 2003 color scheme:

public static class Outlook2003ColorScheme
{
   ...
}

public static class Outlook2007ColorScheme
{
   ...
}

But i'm still faced with the fact that the code depends on the presence of a static class called ColorScheme. My first thought was to create a ColorScheme class that i will descend from either Outlook2003 or Outlook2007:

public static class ColorScheme : Outlook2007ColorScheme
{
}

but you cannot descend from a static class.

My next thought was to create the static ColorScheme class, but make Outlook2003ColorScheme and Outlook2007ColorScheme classes non-static. Then a static variable in the static ColorScheme class can point to either "true" color scheme:

public static class ColorScheme
{
    private static CustomColorScheme = new Outlook2007ColorScheme();
    ...
}

private class CustomColorScheme 
{ 
   ...
}

private class Outlook2008ColorScheme : CustomColorScheme 
{
    ...
}

private class Outlook2003ColorScheme : CustomColorScheme 
{
   ...
}

but that would require me to convert a class composed entirly of readonly static Colors into overridable properties, and then my ColorScheme class would need to have the 30 different property getters thunk down into the contained object.

That's just too much typing.

So my next thought was to alias the class:

public static ColorScheme = Outlook2007ColorScheme;

But that doesn't compile.

How can i alias a static class into another name?

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Update: Can someone please add the answer "You cannot do this in C#", so i can mark that as the accepted answer. Anyone else wanting the answer to the same question will find this question, the accepted answer, and a number of workarounds that might, or might not, be useful.

i just want to close this question out.

Answer 1

You cannot alias a class name in C#.

There are things you can do that are not aliasing a class name in C#.

But to answer the original question: you cannot alias a class name in C#.

---

Update: People are confused why using doesn't work. Example:

Form1.cs

private void button1_Click(object sender, EventArgs e)
{
   this.BackColor = ColorScheme.ApplyColorScheme(this.BackColor);
}

ColorScheme.cs

class ColorScheme
{
    public static Color ApplyColorScheme(Color c) { ... }
}

And everything works. Now i want to create a new class, and alias ColorScheme to it (so that no code needs to be modified):

ColorScheme.cs

using ColorScheme = Outlook2007ColorScheme;

class Outlook2007ColorScheme
{
    public static Color ApplyColorScheme(Color c) { ... }
}

Ohh, i'm sorry. This code doesn't compile:

My question was how to alias a class in C#. It cannot be done. There are things i can do that are not aliasing a class name in C#:

• change everyone who depends on ColorScheme to using ColorScheme instead (code change workaround because i cannot alias)
• change everyone who depends on ColorScheme to use a factory pattern them a polymorphic class or interface (code change workaround because i cannot alias)

But these workarounds involve breaking existing code: not an option.

If people depend on the presence of a ColorScheme class, i have to actually copy/paste a ColorScheme class.

In other words: i cannot alias a class name in C#.

This contrasts with other object oriented languages, where i could define the alias:

ColorScheme = Outlook2007ColorScheme

and i'd be done.

Answer 2

If you change the original class name, you could rewrite the dependent code using an import alias as a typedef substitute:

using ColorScheme = The.Fully.Qualified.Namespace.Outlook2007ColorScheme;

This has to go at the top of the file/namespace, just like regular usings.

I don't know if this is practical in your case, though.

Answer 3

You can make an alias for your class by adding this line of code:

using Outlook2007ColorScheme = YourNameSpace.ColorScheme;

Answer 4

You want a (Factory|Singleton), depending on your requirements. The premise is to make it so that the client code doesn't have to know which color scheme it is getting. If the color scheme should be application wide, a singleton should be fine. If you may use a different scheme in different circumstances, a Factory pattern is probably the way to go. Either way, when the color scheme needs to change, the code only has to be changed in one place.

public interface ColorScheme {
    Color TitleBar { get; }
    Color Background{ get; }
    ...
}

public static class ColorSchemeFactory {

    private static ColorScheme scheme = new Outlook2007ColorScheme();

    public static ColorScheme GetColorScheme() { //Add applicable arguments
        return scheme;
    }
}

public class Outlook2003ColorScheme: ColorScheme {
   public Color TitleBar {
       get { return Color.LightBlue; }
   }

    public Color Background {
        get { return Color.Gray; }
    }
}

public class Outlook2007ColorScheme: ColorScheme {
   public Color TitleBar {
       get { return Color.Blue; }
   }

    public Color Background {
        get { return Color.White; }
    }
}

Answer 5

try this:

using ColorScheme=[fully qualified].Outlook2007ColorScheme

Answer 6

I'm adding this comment for users finding this long after OP accepted their "answer". Aliasing in C# works by specifying the class name using it's fully qualified namespace. One defined, the alias name can be used within it's scope. Example.

using aliasClass = Fully.Qualified.Namespace.Example;
//Example being the class in the Fully.Qualified.Namespace

public class Test{

  public void Test_Function(){

    aliasClass.DoStuff();
    //aliasClass here representing the Example class thus aliasing
    //aliasClass will be in scope for all code in my Test.cs file
  }

}

Apologies for the quickly typed code but hopefully it explains how this should be implemented so that users aren't mislead into believing it cannot be done in C#.

Answer 7

Aliasing the way that you would like to do it will not work in C#. This is because aliasing is done through the using directive, which is limited to the file/namespace in question. If you have 50 files that use the old class name, that will mean 50 places to update.

That said, I think there is an easy solution to make your code change as minimal as possible. Make the ColorScheme class a facade for your calls to the actual classes with the implementation, and use the using in that file to determine which ColorScheme you use.

In other words, do this:

using CurrentColorScheme = Outlook2007ColorScheme;
public static class ColorScheme
{
   public static Color ApplyColorScheme(Color c)
   {
       return CurrentColorScheme.ApplyColorScheme(c);
   }
   public static Something DoSomethingElse(Param a, Param b)
   {
       return CurrentColorScheme.DoSomethingElse(a, b);
   }
}

Then in your code behind, change nothing:

private void button1_Click(object sender, EventArgs e)
{
   this.BackColor = ColorScheme.ApplyColorScheme(this.BackColor);
}

You can then update the values of ColorScheme by updating one line of code (using CurrentColorScheme = Outlook2008ColorScheme;).

A couple concerns here:

• Every new method or property definition will then need to be added in two places, to the ColorScheme class and to the Outlook2007ColorScheme class. This is extra work, but if this is true legacy code, it shouldn't be a frequent occurence. As a bonus, the code in ColorScheme is so simple that any possible bug is very obvious.
• This use of static classes doesn't seem natural to me; I probably would try to refactor the legacy code to do this differently, but I understand too that your situation may not allow that.
• If you already have a ColorScheme class that you're replacing, this approach and any other could be a problem. I would advise that you rename that class to something like ColorSchemeOld, and then access it through using CurrentColorScheme = ColorSchemeOld;.

Answer 8

I suppose you can always inherit from the base class with nothing added

public class Child : MyReallyReallyLongNamedClass {}

UPDATE

But if you have the capability of refactoring the class itself: A class name is usually unnecessarily long due to lack of namespaces.

If you see cases as ApiLoginUser, DataBaseUser, WebPortalLoginUser, is usually indication of lack of namespace due the fear that the name User might conflict.

In this case however, you can use namespace alias ,as it has been pointed out in above posts

using LoginApi = MyCompany.Api.Login;
using AuthDB = MyCompany.DataBase.Auth;
using ViewModels = MyCompany.BananasPortal.Models;

// ...
AuthDB.User dbUser;
using ( var ctxt = new AuthDB.AuthContext() )
{
    dbUser = ctxt.Users.Find(userId);
}

var apiUser = new LoginApi.Models.User {
        Username = dbUser.EmailAddess,
        Password = "*****"
    };

LoginApi.UserSession apiUserSession = await LoginApi.Login(apiUser);
var vm = new ViewModels.User(apiUserSession.User.Details);
return View(vm);

Note how the class names are all User, but in different namespaces. Quoting PEP-20: Zen of Python:

Namespaces are one honking great idea -- let's do more of those!

Hope this helps

Answer 9

Is it possible to change to using an interface?

Perhaps you could create an IColorScheme interface that all of the classes implement?

This would work well with the factory pattern as shown by Chris Marasti-Georg

Answer 10

It's a very late partial answer - but if you define the same class 'ColorScheme', in the same namespace 'Outlook', but in separate assemblies, one called Outlook2003 and the other Outlook2007, then all you need to do is reference the appropriate assembly.