Question

This time, I’m gonna create a math problems. I plan to have a dictionary where the key is Levels enum {Easy, Medium, Hard} and value should contain some configuration about how to create the problems.

For example:

BinaryProblemConfiguration
    + Bound1 : Bound<int>
    + Bound2 : Bound<int>

Bound has two properties: min and max.

Others types of problems don’t need Bounds, but need other data.

So, I was thinking create a interface called IConfiguration.

public interface IConfiguration {}

And concrete Configurations should be:

public class BinaryProblemConfiguration : IConfiguration
{
    public Bound Bound1 {get;set;}
    public Bound Bound2 {get;set;}
}

public class AnotherProblemConfiguration : IConfiguration
{
    // other stuff
}

The idea is to have a dictionary called ConfigurationLevels. Is this a good practice left the interface empty or means is wrong with my design?

Answer 1

The .NET Framework Design Guidelines calls this a “marker” interface and definitely says that it is a bad idea. They recommned using a custom Attribute instead.

Avoid using marker interfaces (interfaces with no members).

Custom attributes provide a way to mark a type. For more information
about custom attributes, see Writing Custom Attributes. Custom
attributes are preferred when you can defer checking for the attribute
until the code is executing. If your scenario requires compile-time
checking, you cannot comply with this guideline.

http://msdn.microsoft.com/en-us/library/ms229022.aspx

public sealed class ConfigurationAttribute : Attribute {

}


[ConfigurationAttribute]
public class AnotherProblemConfiguration : IConfiguration 
{ 
    // other stuff 
}