How do you put a Func in a C# attribute (annotation)?

Question

I have a C# annotation which is :

[AttributeUsage(AttributeTargets.Method)]
public class OperationInfo : System.Attribute {
    public enum VisibilityType {
         


        

Answer 1

From the C# spec:

17.1.3 Attribute parameter types

The types of positional and named parameters for an attribute class are limited to the attribute parameter types, which are:

· One of the following types: bool, byte, char, double, float, int, long, sbyte, short, string, uint, ulong, ushort.

· The type object.

· The type System.Type.

· An enum type, provided it has public accessibility and the types in which it is nested (if any) also have public accessibility (§17.2).

· Single-dimensional arrays of the above types.

Answer 2

I don't think it is possible, c# only allows you to use Attributes with constant values only.

One way of doing this would be to create a class instead of a func, and then you pass the type of that class into the attribute. You'd then need to instantiate it with reflection and execute a method in it.

So an example would be:

public interface IDoStuff
{
    IList<string> Execute();
}

then your attribute would take a type instead of a Func

public OperationInfo(VisibilityType v, string title, Type type)
{
   ///...
}

you then would create a class that implements your interface and pass it into the attribute. Although this would mean that (at least initially, and without knowing your problem) you will need to create a new class every time you want to return different results.