Polymorphic Enums for state handling

Question

how do i handle Enums without using switch or if statements in C#?

For Example

enum Pricemethod
{
    Max,
    Min,
    Average
}

... and i have a class Article

 public class Article 
{
    private List<Double> _pricehistorie;

    public List<Double> Pricehistorie
    {
        get { return _pricehistorie; }
        set { _pricehistorie = value; }
    }

    public Pricemethod Pricemethod { get; set; }

    public double Price
    {
        get {
            switch (Pricemethod)
            {
                case Pricemethod.Average: return Average();
                case Pricemethod.Max: return Max();
                case Pricemethod.Min: return Min();
            }

        }
    }

}

i want to avoid the switch statement and make it generic.

For a specific Pricemethod call a specific Calculation and return it.

get { return CalculatedPrice(Pricemethod); }

Wich pattern is to use here and maybe someone have a good implementation idea. Searched already for state pattern, but i dont think this is the right one.

Answer 1

how do I handle enums without using switch or if statements in C#?

You don't. enums are just a pleasant syntax for writing const int.

Consider this pattern:

public abstract class PriceMethod
{
  // Prevent inheritance from outside.
  private PriceMethod() {}

  public abstract decimal Invoke(IEnumerable<decimal> sequence);

  public static PriceMethod Max = new MaxMethod();

  private sealed class MaxMethod : PriceMethod
  {
    public override decimal Invoke(IEnumerable<decimal> sequence)
    {
      return sequence.Max();
    }
  }

  // etc, 
}

And now you can say

public decimal Price
{
    get { return PriceMethod.Invoke(this.PriceHistory); }
}

And the user can say

myArticle.PriceMethod = PriceMethod.Max;
decimal price = myArticle.Price;

Answer 2

You could create an interface, and classes that implement it:

public interface IPriceMethod
{
    double Calculate(IList<double> priceHistorie);
}
public class AveragePrice : IPriceMethod
{
    public double Calculate(IList<double> priceHistorie)
    {
        return priceHistorie.Average();
    }
}
// other classes
public class Article 
{
    private List<Double> _pricehistorie;

    public List<Double> Pricehistorie
    {
        get { return _pricehistorie; }
        set { _pricehistorie = value; }
    }

    public IPriceMethod Pricemethod { get; set; }

    public double Price
    {
        get {
            return Pricemethod.Calculate(Pricehistorie);
        }
    }

}

Edit: another way is using a Dictionary to map Funcs, so you don't have to create classes just for this (this code is based on code by Servy, who since deleted his answer):

public class Article
{
    private static readonly Dictionary<Pricemethod, Func<IEnumerable<double>, double>>
        priceMethods = new Dictionary<Pricemethod, Func<IEnumerable<double>, double>>
        {
            {Pricemethod.Max,ph => ph.Max()},
            {Pricemethod.Min,ph => ph.Min()},
            {Pricemethod.Average,ph => ph.Average()},
        };

    public Pricemethod Pricemethod { get; set; }
    public List<Double> Pricehistory { get; set; }

    public double Price
    {
        get
        {
            return priceMethods[Pricemethod](Pricehistory);
        }
    }
}