How to switch between "possible" type of an object? [duplicate]

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Possible Duplicate:

C# - Is there a better alternative than this to ‘switch on type’?

My company legacy code has something as follow

public override Uri GetUri(object obj)
{
    if ((obj is Entry) || (obj is EntryComment))
    {
        //
    }
    if (obj is Blog)
    {
        //
    }

    // if obj is blah blah blah
}

This method is just ugly. I want to refactor it, but I don't know a technique to iterate over "possible" types that obj can be.

How can I refactor this?

Thank you.

---

A couple of options:

• If you're using C# 4, you could use dynamic typing, and split the method into a number of overloads:

  public Uri GetUri(dynamic obj)
  {
      return GetUriImpl(obj);
  }
  
  private Uri GetUriImpl(Entry entry)
  {
      ...
  }
  
  private Uri GetUriImpl(EntryComment comment)
  {
      ...
  }
  

  In this case you'd probably want some sort of "backstop" method in case it's not a known type.

• You could create a Dictionary<Type, Func<object, Uri>>:

  private static Dictionary<Type, Func<object, Uri>> UriProviders = 
      new Dictionary<Type, Func<object, Uri>> {   
      { typeof(Entry), value => ... },
      { typeof(EntryComment), value => ... },
      { typeof(Blog), value => ... },
  };
  

  and then:

  public Uri GetUri(object obj)
  {
      Func<object, Uri> provider;
      if (!UriProviders.TryGetValue(obj.GetType(), out provider))
      {
          // Handle unknown type case
      }
      return provider(obj);
  }
  

  Note that this won't cover the case where you receive a subtype of Entry etc.

Neither of these are particularly nice, mind you... I suspect a higher level redesign may be preferable.

---

You can also refactor this with interfaces

public interface IHasUri
{
   public Uri GetUri();
}

and implement this interface in all you hierarchy. Than you can use

public Uri GetUri(object obj)
{
    IHasUri hasUri = obj as IHasUri;
    if(hasUri != null)
      Uri uri = hasUri.GetUri();

    // bla bla bla 
}

---

I think Lasse V. Karlsen has the right of it in his comments, a redesign is more appropriate perhaps

You could create an interface like Stecya suggests

public interface IUriAccessible { //or some sort of a more descriptive name
    Uri Url {get;}
}

and then for each object that you care for, eg Entry, you could

public class Entry:IUriAccessible {
    //... other code here
    public Uri Url {
        get {
            //return uri here
        }
    }
}

and now you can just call it on the object

var entry = new Entry();
var uri = entry.Url;

---

You can have a List<Type>() with all types you want to check for and iterate that list. but I don't think that makes the code faster.

---

You can't switch-case types.

A switch expression or case label must be a bool, char, string, integral, enum, or corresponding nullable type