Question

Given an example such as ..

public interface IInterface { }

public static void Insert<T>(this IList<T> list, IList<T> items) where T : IInterface
{
 // ... logic
}

This works fine, but I was wondering if it is possible to use an Attribute as a constraint. Such as …

class InsertableAttribute : Attribute

public static void Insert<T>(this IList<T> list, IList<T> items) where T : [Insertable]
{
 // ... logic
}

Obviously this syntax doesn’t work, or I wouldn’t be posting the question. But I’m just curious if it is possible or not, and how to do it.

Answer 1

No. You can only use (base)classes and interfaces as constraints.

You can however do something like this:

public static void Insert<T>(this IList<T> list, IList<T> items)
{
    var attributes = typeof(T).GetCustomAttributes(typeof(InsertableAttribute), true);

    if (attributes.Length == 0)
        throw new ArgumentException("T does not have attribute InsertableAttribute");

    /// Logic.
}