How can I use Generics to create a way of making an IEnumerable from an enum?

Question

Given an enum like this:

public enum City {
    London    = 1,
    Liverpool  = 20,
    Leeds       = 25
}

public enum House {
    OneFloor    = 1,
    TwoF         


        

Answer 1

This function might help you:

public static IEnumerable<KeyValuePair<int, string>> GetValues<T>() where T : struct
{
        var t = typeof(T);
        if(!t.IsEnum)
            throw new ArgumentException("Not an enum type");

        return Enum.GetValues(t).Cast<T>().Select (x => 
               new KeyValuePair<int, string>(
                   (int)Enum.ToObject(t, x), 
                    x.ToString()));
}

Usage:

var values = GetValues<City>();

Answer 2

Why not:

    IEnumerable<object> GetValues<T>()
    {
        return Enum.GetValues(typeof (T))
                   .Cast<T>()
                   .Select(value => new {     
                                             value = Convert.ToInt32(value),
                                             name = value.ToString()
                                         });

    }

So you can use:

var result = GetValues<City>();

If you would like to make constraint generic T as enum, because enum cannot be used as generic contraint directly, but enum inherits from interface IConvertible, believe this way is okay:

IEnumerable<object> GetValues<T>() where T: struct, IConvertible
{}

To replace IEnumerable<object> by Dictionary:

Dictionary<int, string> GetValues<T>() where T :  struct, IConvertible
{
    return Enum.GetValues(typeof (T)).Cast<T>()
               .ToDictionary(value => Convert.ToInt32(value),
                             value => value.ToString());
}

Edit: As Magnus's comment, if you need to make sure the order of items, Dictionary is not the option. Define your own strong type would be better.

Answer 3

Use Jon Skeet's unconstrained melody.

using UnconstrainedMelody;

---

You can put your enum values into a Dictionary<int, string> and then enumerate over them:

var valuesAsDictionary = Enums.GetValues<City>()
                              .ToDictionary(key => (int)key, value => value.ToString());

---

But you probably don't even need to do that. Why not just enumerate over the values directly:

foreach (var value in Enums.GetValues<City>())
{
    Console.WriteLine("{0}: {1}", (int)value, value);
}