Creating a non-generic function for adding items to a HashSet<T>

Question

In my C# program, I want to add items to a HashSet<T> via reflection. With a List<T> this is not a problem because I can cast the list to the non-generic IList interface:

foreach (PropertyInfo property in myClass.GetType().GetProperties())
{
    object value = property.GetValue(myClass);
    IList valueAsIList = value as IList;
    if (valueAsIList != null)
        valueAsIList.Add(item2Insert);
}

Now I want to do the same thing with HashSet<T> but there is no non-generic contract like IList that I could cast it to and call the Add method. Is there any other way to do it?

Answer 1

Since you already are using reflection, why not try to lookup the Add method?

var addMethod = value.GetType().GetMethods().FirstOrDefault(m => m.Name == "Add");

//validate this method; has it been found? What should we do if it didnt? Maybe it should be SingleOrDefault

addMethod.Invoke(value, valueToAdd)

Maybe add more validations and what not.. :)

Answer 2

You could solve this with dynamic . It will "take care of" the reflection work for you.

using System;
using System.Collections.Generic;

namespace Bob
{
    public class Program
    {
        static void Main(string[] args)
        {
            var hash = new HashSet<int>();
            Console.WriteLine(hash.Count);
            Add(hash);
            Console.WriteLine(hash.Count);
            Console.ReadLine();
        }

        private static void Add(dynamic hash)
        {
            hash.Add(1);
        }
    }
}