using System;

using System.Collections.Generic;

using System.Linq.Expressions;

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        List<User> userCollection = new List<User>() {

            new User { Id = 1, Name = "Bob", Age = 2 },

            new User { Id = 2, Name = "Dave", Age = 30 },

            new User { Id = 3, Name = "Jane", Age = 42 },

            new User { Id = 4, Name = "Anne", Age = 12 }

        };

        List<KeyValue> list = ReadCollection(userCollection, "Id", "Name");

        foreach(var x in list)

        {

            Console.WriteLine("{0}: {1}", x.Key, x.Value);

        }

    }

​

    private static List<KeyValue> ReadCollection<T>(IList<T> collection, string keyName, string valueName)

    {       

        List<KeyValue> list = new List<KeyValue>();

​

        Func<T, int> keyFunction = GenerateLambda<T, int>(keyName);

        Func<T, string> valueFunction = GenerateLambda<T, string>(valueName);

​

        for (int i = 0; i < collection.Count; i++)

        {

            T elem = collection[i];

            int key = keyFunction(elem);

            string value = valueFunction(elem);

            list.Add(new KeyValue(key, value));

        }

        return list;

​

        // or simpler

        //return collection.Select(elem => new KeyValue(keyFunction(elem), valueFunction(elem))).ToList();

    }

    private static Func<T, TProp> GenerateLambda<T, TProp>(string propertyName)

    {

        var p = Expression.Parameter(typeof(T));

        var expr = Expression.Lambda<Func<T, TProp>>(Expression.PropertyOrField(p, propertyName), p);

        return expr.Compile();

    }

}

​

public class User{

    public int Id { get; set; }

    public string Name { get; set; }

    public short Age { get; set; }

}

​

public class UserCollection: List<User> {

}

​

public class KeyValue

{

    public int Key {get; private set;}

    public string Value {get; private set;}

    public KeyValue(int key, string value)

    {

        this.Key = key;

        this.Value = value;

    }

}