The definition of CharArraySet is dangerously confusing and leads to bugs when
used.
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Key: LUCENENET-414
URL: https://issues.apache.org/jira/browse/LUCENENET-414
Project: Lucene.Net
Issue Type: Bug
Components: Lucene.Net Core
Affects Versions: Lucene.Net 2.9.2
Environment: Irrelevant
Reporter: Vincent Van Den Berghe
Priority: Minor
Fix For: Lucene.Net 2.9.2
Right now, CharArraySet derives from System.Collections.Hashtable, but doesn't
actually use this base type for storing elements.
However, the StandardAnalyzer.STOP_WORDS_SET is exposed as a
System.Collections.Hashtable. The trivial code to build your own stopword set
using the StandardAnalyzer.STOP_WORDS_SET and adding your own set of stopwords
like this:
CharArraySet myStopWords = new CharArraySet(StandardAnalyzer.STOP_WORDS_SET,
ignoreCase: false);
foreach (string domainSpecificStopWord in DomainSpecificStopWords)
stopWords.Add(domainSpecificStopWord);
... will fail because the CharArraySet accepts an ICollection, which will be
passed the Hashtable instance of STOP_WORDS_SET: the resulting myStopWords will
only contain the DomainSpecificStopWords, and not those from STOP_WORDS_SET.
One workaround would be to replace the first line with this:
CharArraySet stopWords = new CharArraySet(StandardAnalyzer.STOP_WORDS_SET.Count
+ DomainSpecificStopWords.Length, ignoreCase: false);
foreach (string domainSpecificStopWord in
(CharArraySet)StandardAnalyzer.STOP_WORDS_SET)
stopWords.Add(domainSpecificStopWord);
... but this makes use of the implementation detail (the STOP_WORDS_SET is
really an UnmodifiableCharArraySet which is itself a CharArraySet). It works
because it forces the foreach() to use the correct
CharArraySet.GetEnumerator(), which is defined as a "new" method (this has a
bad code smell to it)
At least 2 possibilities exist to solve this problem:
- Make CharArraySet use the Hashtable instance and a custom comparator, instead
of its own implementation.
- Make CharArraySet use HashSet<char[]>, defined in .NET 4.0.
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