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From "Shad Storhaug (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (LUCENENET-469) Convert Java Iterator classes to implement IEnumerable<T>
Date Sun, 23 Apr 2017 23:50:04 GMT

     [ https://issues.apache.org/jira/browse/LUCENENET-469?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Shad Storhaug updated LUCENENET-469:
------------------------------------
    Affects Version/s: Lucene.Net 4.8.0
        Fix Version/s: Lucene.Net 4.8.0

We should probably look into doing this. There are several places in the code base where the
dispose pattern is not used correctly in conjunction with iterators/enumerators.

I am not sure if it makes sense to make every type of iterator into an enumerator. For example
BreakIterator is designed to navigate forward, backward, and to skip to specific points. Perhaps
we could still implement IEnumerable<T> but also create other interfaces with extra
functionality. In any case, this is a major API change that should be looked at before the
4.8.0 release.

> Convert Java Iterator classes to implement IEnumerable<T>
> ---------------------------------------------------------
>
>                 Key: LUCENENET-469
>                 URL: https://issues.apache.org/jira/browse/LUCENENET-469
>             Project: Lucene.Net
>          Issue Type: Sub-task
>          Components: Lucene.Net Contrib, Lucene.Net Core
>    Affects Versions: Lucene.Net 2.9.4, Lucene.Net 2.9.4g, Lucene.Net 3.0.3, Lucene.Net
4.8.0
>         Environment: all
>            Reporter: Christopher Currens
>             Fix For: Lucene.Net 4.8.0
>
>
> The Iterator pattern in Java is equivalent to IEnumerable in .NET.  Classes that were
directly ported in Java using the Iterator pattern, cannot be used with Linq or foreach blocks
in .NET.
> {{Next()}} would be equivalent to .NET's {{MoveNext()}}, and in the below case, {{Term()}}
would be as .NET's {{Current}} property.  In cases as below, it will require {{TermEnum}}
to become an abstract class with {{Term}} and {{DocFreq}} properties, which would be returned
from another class or method that implemented {{IEnumerable<TermEnum>}}.
> {noformat} 
> 	public abstract class TermEnum : IDisposable
> 	{
> 		public abstract bool Next();
> 		public abstract Term Term();
> 		public abstract int DocFreq();
> 		public abstract void  Close();
> 	        public abstract void Dispose();
> 	}
> {noformat} 
> would instead look something like:
> {noformat} 
> 	public class TermFreq
> 	{
> 		public abstract Term { get; }
> 		public abstract int { get; }
> 	}
>         public abstract class TermEnum : IEnumerable<TermFreq>, IDisposable
>         {
>                 // ...
>         }
> {noformat}
> Keep in mind that it is important that if the class being converted implements {{IDisposable}},
the class that is enumerating the terms (in this case {{TermEnum}}) should inherit from both
{{IEnumerable<T>}} *and* {{IDisposable}}.  This won't be any change to the user, as
the compiler automatically calls {{IDisposable}} when used in a {{foreach}} loop.



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