[LUCENENET-515] bring back TokenStream.GetAttribute(Type).

• Type: Improvement
• Status: Resolved
• Priority: Major
• Resolution: Fixed
• Affects Version/s: Lucene.Net 3.0.3
• Fix Version/s: Lucene.Net 3.6
• Component/s: Lucene.Net Core
• Assignee: Unassigned
• Reporter: Jens Melgaard
• Created: 07/Dec/12 12:49
• Updated: 27/Dec/12 21:18
• Resolved: 27/Dec/12 21:18

Description

I Have noticed that TokenStream.GetAttribute(Type) is gone in favor for TokenStream.GetAttribute<Type>();

Obviously TokenStream.GetAttribute<Type>() is a better syntax; but it should not replace TokenStream.GetAttribute(Type), but instead compliment it... But this is a common pitfall, especially for non-.NET developers and people who have not run into the implications of this..

In the case of Lucene.NET, it is properly unlikely that this will affect anyone, however, I consider what has been done bad practice... now why is that?

Many would think like this:

Before I had to do this old thing...

TokenStream.GetAttribute(typeof(TermAttribute));

And god I hated that, so now I replaced it with the much more beautiful:

TokenStream.GetAttribute<TermAttribute>();

And deleted that old hag of a method taking a Type... And now I am happy...

BUT!...

What when...

Type myNotDefinedHereType = GetTypeFromSomeWhere();
TokenSteam.GetAttribute.... ?????!?!?!?... Uhm... What now???? 

Now you have to write a whole lot of reflection mess, use a dynamically compiled delegate using IL-Emit or the Mono Compiler as a Service...
All of those 3 workarounds are generally just ugly...

If you keept both...

Type myNotDefinedHereType = GetTypeFromSomeWhere();
TokenSteam.GetAttribute(myNotDefinedHereType);

While it might be unlikely that it will ever be used, there is always the off case, and API's should support both...

So instead of:

public virtual T GetAttribute<T>() where T : IAttribute
    {
      Type key = typeof (T);
      if (!this.attributes.ContainsKey(key))
        throw new ArgumentException("This AttributeSource does not have the attribute '" + key.FullName + "'.");
      else
        return (T) this.attributes[key].Value;
    }

Do:

public T GetAttribute<T>() where T : IAttribute
{
   return (T) GetAttribute(typeof(T));
} 
public virtual IAttribute GetAttribute(Type key)
    {
      //Note: Since Type is required to implement IAttribute, I would properly check that as well to be able to provide a more meaningfull error... However to speed things up, I would do it inside the if bellow...
      if (!this.attributes.ContainsKey(key))
        throw new ArgumentException("This AttributeSource does not have the attribute '" + key.FullName + "'.");
      else
        return (T) this.attributes[key].Value;
    }