What datatype to use?

I need a collection that

• contains a set of objects linked to a double.
• The sequence of these pairs should be arbitrary set by me (based on an int I get from the database) and be static throughout the lifecycle.
• The number of entries will be small (0 ~ 20) but varying.
• The collection should be itteratable.
• I don't have to search the collection for anything.
• The double will be changed after intialization of the collection.
• I would like to work with existing datatypes (no new classes) since it will be used in my asp.net mvc controllers, views and services and I don't want them to all to have a dependency on a library just for this stupid holder class.

I thought

IDictionary<int, KeyvaluePair<TheType, double>>

would do the trick, but then I can't set the double after init.

--Edit--
I found out that the classes generated by the linq 2 sql visual studio thingy are actually partial classes so you can add to them whatever you want. I solved my question by adding a double field to the partial class.
Thanks all for the answers you came up with.

From stackoverflow

• It sounds like you may just want an equivalent of KeyValuePair, but mutable. Given that you're only using it as a pair of values rather than a key-value pair, you could just do:

  public class MutablePair<TFirst, TSecond>
  {
      public TFirst First { get; set; }
      public TSecond Second { get; set; }
  
      public MutablePair()
      {
      }
  
      public MutablePair<TFirst, TSecond>(TFirst first, TSecond second)
      {
          First = first;
          Second = second;
      }
  }
  

  This doesn't override GetHashCode or Equals, because you're not actually using those (as it's in a value position).

  borisCallens : Your solution is correct, but my requirements weren't complete. Updated them. Could you have a look?

• Well, KeyValuePair is immutable (which is a good thing), so you'll have to replace the entire value of KeyValuePair, not just the part of it:

  yourDict[10] = new KeyValuePair<TheType, Double>(yourDict[10].Key, newValue);
  

  ... or think like Jon Skeet. Gah. :)

• struct MyPair
  {
      public object TheType;
      public double Value;
  }
  
  MyPair[] MyColleccyion = new MyPair[20];
  

  borisCallens : I updated the requirements some.

• How about this

  public class ListThing<TKey, TValue> : Dictionary<TKey, TValue>
  {
      public double DoubleThing { get; set; }
  
      public ListThing(double value)
      {
          DoubleThing = value;
      }
  }