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https://issues.apache.org/jira/browse/LUCENENET-469?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16120627#comment-16120627
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Shad Storhaug commented on LUCENENET-469:
-----------------------------------------

{quote}It's this Enum class I was calling the "collection" type 'cos it kind of 
holds the collection state.

What I was proposing was to make the Enum also look like an IEnumerable so that 
you can foreach over it.
Which means it needs a GetEnumerable() to return an IEnumerator. This new 
enumerator is the EnumEnumerator type from in previous messages.

So, I'm taking an Enum, adding an IEnumerable facade, to return a new 
IEnumerable type which pokes the Enum to move forward.{quote}

That is an interesting idea.

I am not sure if the state is actually being "iterated over" so much as it is 
being calculated on the fly. But then, {{IEnumerable<T>}} is just an interface 
- it doesn't actually define any behavior. In fact, I had to redefine what the 
key and value {{ICollection<T>}} s do in CharArrayMap's KeyCollection and 
ValueCollection, so maybe this is also possible.

> NB: some thought would be needed to define what the "item" class 
> (representing Current) should look like in each case.
> NB: Calling a Current changing method (ie one of the Seek...() methods) from 
> inside a foreach would result in undefined behavior.

So then we end up with some behavior that doesn't fit the mold.

I thought for a moment that it could be possible these SeekCeil and SeekExact 
methods are only defined here because there are no such thing as extension 
methods in Java, but since they are overridden in subclasses, that is probably 
not a valid assumption.

Speaking of which, I suggest you have a look at how they are used in the 
TermsEnum overloads in the codecs (for example 
[Lucene40TermVectorsReader](https://github.com/apache/lucenenet/blob/468199e3fa95c7e1f77b14e7f00aeaafd7c2f8b9/src/Lucene.Net/Codecs/Lucene40/Lucene40TermVectorsReader.cs#L446))
 or 
[Lucene45DocValuesProducer.TermsEnumAnonymousInnerClassHelper](https://github.com/apache/lucenenet/blob/468199e3fa95c7e1f77b14e7f00aeaafd7c2f8b9/src/Lucene.Net/Codecs/Lucene45/Lucene45DocValuesProducer.cs#L1090).

As you can see, the complexity of these enums becomes quite high (lots of 
internal state), and it seems to me it would be simpler to port future changes 
from Lucene if the general structure of the "extras" (that is, the properties 
and Seek* methods) were left alone (or at least left intact and used by some 
other type of facade). The DocsAndPositionsEnum s are even more complex than 
this.

The only thing I was hoping to get out of this was the added ability to use a 
foreach loop on Terms (and possibly the DocIdSetIterator). Sure we could 
refactor the TermsEnum data structure to be more .NET-like, but then where 
would we be when we need to connect the dots on the next Lucene upgrade? I am 
not necessarily against it, but finding bugs in the codec code is no picnic, so 
we would need some clear way to ensure future codecs behavior can be mapped 
onto the new structure without causing too much pain. Keep in mind, the codecs 
change in every major (and nearly every minor) version.

{quote}Phew... Did that make sense; fit with your view of the universe?{quote}

Wow, do I sound so closed minded? I think I need to work on my delivery :). 

> 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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