Use the feature of calling .Add during initialization

CustomClassInitialization.cs

using System;
using System.Collections;

public class Test
{
	public static void Main()
	{
		new MyClass{1, "a", {2, "b"}}; //calls Add(1), Add("a"), Add(2, "a")
	}
}

public sealed class MyClass : IEnumerable
{
	public void Add(int i)
	{
		Console.WriteLine("Added an int " + i);
	}
	
	public void Add(String s)
	{
		Console.WriteLine("Added a string " + s);
	}
	
	public void Add(int i, String s)
	{
		Console.WriteLine("Added a pair (" + i + ", " + s + ")");
	}
	
	public IEnumerator GetEnumerator()
	{
		throw new NotSupportedException(); 
	}
}