Why does my .NET Attribute not perform an action?

Question

I've created a simple Attribute:

[AttributeUsage(AttributeTargets.Method)]
public class InitAttribute : System.Attribute
{
    public InitAttribute()
    {
        Console.WriteLine("Works!");
    }
}

and I apply it to a simple method:

static class Logger
{
    public static string _severity;

    public static void Init(string severity)
    {
        _severity = severity;
    }

    [Init()]
    public static void p()
    {
        Console.WriteLine(_severity);
    }
}

What is going on is pretty straightforward. Only, I expect the attribute to perform an action (printing "Works!"), but this does not happen.

Additionally, printing "Works!" is of course just for debugging purposes: I'd like to access the instance's property _severity (to check if is != null, for example), but everything I keep reading about regarding attributes (that is pretty new to me) is about accessing the class' methods or properties and so on via reflection. Once I've evaluated _severity, how can I modify the behavior of the decorated method (in this case, raise an exception "Logger is not initialized" and do not execute it)?

Any help appreciated.

Answer 1

If you need to perform an action as control enters a method, you should look at aspect-oriented programming and frameworks such as PostSharp. Attributes are not designed to perform anything by themselves. They are just a bunch of data (or metadata if you will) attached to stuff in IL assemblies that can be queried at runtime.