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From Andy Pook <andy.p...@gmail.com>
Subject Re: [Lucene.Net] [jira] [Created] (LUCENENET-469) Convert Java Iterator classes to implement IEnumerable<T>
Date Fri, 08 Jun 2012 19:25:57 GMT
If we don't want to add IEnumerable (though it seems that IEnumerable could
be added in parallel with the existing pattern) could we add a bunch of
extension methods?
Something like the following...

{noformat}
public static class LuceneExtensions
{
public static IEnumerable<Term> GetEnumerable(this TermEnum termEnum)
{
yield return termEnum.Term();
while (termEnum.Next())
yield return termEnum.Term();
}
}
{noformat}

Then you can...
{noformat}
foreach(var e in myTernEnum.GetEnumerable())
{
    // do stuff with e
}
{noformat}

Not as elegant as a direct implementation but gives easy enough access to
foreach sematics.


The second option is to realize that you don't need to explicitly implement
IEnumerable. You just need a GetEnumerator method.
So just add...

{noformat}
public IEnumerable<Term> GetEnumerator()
{
yield return Term();
while (Next())
yield return Term();
}
{noformat}

Now you get nice foreach sematics without even mentioning IEnumerable.
Compiler magic is your friend :-)

BTW: Dispose() is only called automatically when exiting a using block.
Exiting a foreach will not.

Cheers,
  Andy

On 24 January 2012 06:37, Christopher Currens (Created) (JIRA) <
jira@apache.org> wrote:

> 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 3.0.3, Lucene.Net 2.9.4g
>         Environment: all
>            Reporter: Christopher Currens
>             Fix For: Lucene.Net 3.0.3
>
>
> 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.
>
> --
> This message is automatically generated by JIRA.
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> administrators:
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>
>
>

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