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From "Christopher Currens (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (LUCENENET-515) bring back TokenStream.GetAttribute(Type).
Date Sun, 09 Dec 2012 21:57:21 GMT

    [ https://issues.apache.org/jira/browse/LUCENENET-515?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13527639#comment-13527639
] 

Christopher Currens commented on LUCENENET-515:
-----------------------------------------------

Two lines of reflection code isn't what I would consider a "whole lot of reflection mess"
to get what you want done.

{code}
    public static class AttributeSourceExtensions
    {
        public static IAttribute GetAttribute(this AttributeSource attributeSource, Type t)
        {
            if(!typeof(IAttribute).IsAssignableFrom(t))
                throw new ArgumentException("Type of T must inherit from IAttribute");

            var mi = typeof(AttributeSource).GetMethod("GetAttribute").MakeGenericMethod(t);
            return (IAttribute)mi.Invoke(attributeSource, null);
        }
    }
{code}

You could easily do the same for {{HasAttribute}}.  Here's an example:

{code}
        private static void Main(string[] args)
        {
            string str = "This is my text";
            var a = new StandardAnalyzer(Version.LUCENE_30);

            var ts = a.TokenStream("Field", new StringReader(str));

            ts.IncrementToken();

            Console.WriteLine(ts.GetAttribute<ITermAttribute>().Term);
            Console.WriteLine(((ITermAttribute) ts.GetAttribute(typeof(ITermAttribute))).Term);
        }
{code}

I'm not saying that the API shouldn't have an overload that accepts a type, in fact I agree
that it should.  HOWEVER, Lucene 3.0.3 doesn't have a method like this in java, and so that
is the reason why it was removed.  Keep in mind that things run slowly around here, and so
I'm not sure if or when this additional overload will be added for 3.0.3.
                
> bring back TokenStream.GetAttribute(Type).
> ------------------------------------------
>
>                 Key: LUCENENET-515
>                 URL: https://issues.apache.org/jira/browse/LUCENENET-515
>             Project: Lucene.Net
>          Issue Type: Improvement
>          Components: Lucene.Net Core
>    Affects Versions: Lucene.Net 3.0.3
>            Reporter: Jens Melgaard
>
> 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...
> {code}TokenStream.GetAttribute(typeof(TermAttribute));{code}
> And god I hated that, so now I replaced it with the much more beautiful:
> {code}TokenStream.GetAttribute<TermAttribute>();{code}
> And deleted that old hag of a method taking a Type... And now I am happy...
> BUT!...
> What when...
> {code}
> Type myNotDefinedHereType = GetTypeFromSomeWhere();
> TokenSteam.GetAttribute.... ?????!?!?!?... Uhm... What now???? 
> {code}
> 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...
> {code}
> Type myNotDefinedHereType = GetTypeFromSomeWhere();
> TokenSteam.GetAttribute(myNotDefinedHereType);
> {code}
> 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:
> {code}
> 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;
>     }
> {code}
> Do:
> {code}
> 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;
>     }
> {code}

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