c# - How to avoid switch-case in a factory method of child classes

Question

Lets say we have a family of classes (cards, for the sake of it), and we need to instantiate them based on some identifier. A factory method would look like this:

public Card GetCard(int cardNumber) 
{
   switch(cardNumber) 
   {
     case 13: return new King();
     case 12: return new Queen();
     case 11: return new Jack();          
   }

   //...
}

What I want is to avoid this switch. Why? Maybe I want to reuse this comparison in the feature.

What I came up with is something like this:

private Dictionary<int, Type> cardTypes = 
 { 
   {13, typeof(King)},
   {12, typeof(Queen)},
   {11, typeof(Jack)}
 };

 public Card GetCard(int cardNumber) 
 {        
    var cardType = cardTypes[cardNumber];
    var instance = Activator.CreateInstance(cardType);
    return (Card)instance;
 }

However, this solution uses reflection which is expensive, and is also problematic when you have more than one "identifier" (for example 1 and 14 both give Ace - should I add 2 keys to the dictionary?).

What's the best practice in this scenario?

Answer 1

Instead of storing the type in the dictionary, you could store a Func<Card>:

private Dictionary<int, Func<Card>> cardFactories = 
{
    { 13, () => new King() },
    // etc
}

public Card GetCard(int cardNumber) 
{        
    var factory = cardFactories[cardNumber];
    return factory();
}

In the case of cards, I'd probably make them immutable to start with and just populate the dictionary with the cards themselves, but that's a different matter :)