add SentenceContext clone and duplicate

libwccl/sentencecontext.cpp

@@ -7,4 +7,16 @@ SentenceContext::SentenceContext(const boost::shared_ptr<Corpus2::Sentence>& s)
 {
 }
 
+SentenceContext SentenceContext::duplicate() const
+{
+	SentenceContext dup(*this);
+	dup.sentence_.reset(sentence_->clone());
+	return dup;
+}
+
+SentenceContext* SentenceContext::clone() const
+{
+	return new SentenceContext(duplicate());
+}
+
 } /* end ns Wccl */

libwccl/sentencecontext.h

@@ -9,13 +9,20 @@ namespace Wccl {
 /**
  * A wrapper for a Corpus2 Sentence that adds a "current position"
  * and several convenience functions.
+ *
+ * Copying contexts is cheap and safe since the sentence is kept through
+ * a shared pointer, use duplicate() or clone() to get a copy with a separate
+ * underlying sentence (which is slower).
  */
 class SentenceContext
 {
 public:
-	/// Constructor, wraps the Sentence and stes position to 0
+	/// Constructor, wraps the Sentence and sets position to 0
 	SentenceContext(const boost::shared_ptr<Corpus2::Sentence>& s);
 
+	/// Returns a copy of this with a cloned underlyiong sentence
+	SentenceContext duplicate() const;
+
 	/// Cloning -- clones the underlying sentence as well
 	SentenceContext* clone() const;
 
@@ -97,6 +104,8 @@ private:
 	int position_;
 };
 
+// TODO ConstSentenceContext ?
+
 } /* end ns Wccl */
 
 #endif // LIBWCCL_SENTENCECONTEXT_H