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+// Copyright (C) 2016 and later: Unicode, Inc. and others.
+// License & terms of use: http://www.unicode.org/copyright.html
+/*
+**********************************************************************
+* Copyright (C) 1999-2010, International Business Machines Corporation and others.
+* All Rights Reserved.
+**********************************************************************
+* Date Name Description
+* 11/17/99 aliu Creation.
+**********************************************************************
+*/
+#ifndef UNIFILT_H
+#define UNIFILT_H
+
+#include "unicode/unifunct.h"
+#include "unicode/unimatch.h"
+
+/**
+ * \file
+ * \brief C++ API: Unicode Filter
+ */
+
+U_NAMESPACE_BEGIN
+
+/**
+ * U_ETHER is used to represent character values for positions outside
+ * a range. For example, transliterator uses this to represent
+ * characters outside the range contextStart..contextLimit-1. This
+ * allows explicit matching by rules and UnicodeSets of text outside a
+ * defined range.
+ * @stable ICU 3.0
+ */
+#define U_ETHER ((UChar)0xFFFF)
+
+/**
+ *
+ * <code>UnicodeFilter</code> defines a protocol for selecting a
+ * subset of the full range (U+0000 to U+10FFFF) of Unicode characters.
+ * Currently, filters are used in conjunction with classes like {@link
+ * Transliterator} to only process selected characters through a
+ * transformation.
+ *
+ * <p>Note: UnicodeFilter currently stubs out two pure virtual methods
+ * of its base class, UnicodeMatcher. These methods are toPattern()
+ * and matchesIndexValue(). This is done so that filter classes that
+ * are not actually used as matchers -- specifically, those in the
+ * UnicodeFilterLogic component, and those in tests -- can continue to
+ * work without defining these methods. As long as a filter is not
+ * used in an RBT during real transliteration, these methods will not
+ * be called. However, this breaks the UnicodeMatcher base class
+ * protocol, and it is not a correct solution.
+ *
+ * <p>In the future we may revisit the UnicodeMatcher / UnicodeFilter
+ * hierarchy and either redesign it, or simply remove the stubs in
+ * UnicodeFilter and force subclasses to implement the full
+ * UnicodeMatcher protocol.
+ *
+ * @see UnicodeFilterLogic
+ * @stable ICU 2.0
+ */
+class U_COMMON_API UnicodeFilter : public UnicodeFunctor, public UnicodeMatcher {
+
+public:
+ /**
+ * Destructor
+ * @stable ICU 2.0
+ */
+ virtual ~UnicodeFilter();
+
+ /**
+ * Returns <tt>true</tt> for characters that are in the selected
+ * subset. In other words, if a character is <b>to be
+ * filtered</b>, then <tt>contains()</tt> returns
+ * <b><tt>false</tt></b>.
+ * @stable ICU 2.0
+ */
+ virtual UBool contains(UChar32 c) const = 0;
+
+ /**
+ * UnicodeFunctor API. Cast 'this' to a UnicodeMatcher* pointer
+ * and return the pointer.
+ * @stable ICU 2.4
+ */
+ virtual UnicodeMatcher* toMatcher() const;
+
+ /**
+ * Implement UnicodeMatcher API.
+ * @stable ICU 2.4
+ */
+ virtual UMatchDegree matches(const Replaceable& text,
+ int32_t& offset,
+ int32_t limit,
+ UBool incremental);
+
+ /**
+ * UnicodeFunctor API. Nothing to do.
+ * @stable ICU 2.4
+ */
+ virtual void setData(const TransliterationRuleData*);
+
+ /**
+ * ICU "poor man's RTTI", returns a UClassID for this class.
+ *
+ * @stable ICU 2.2
+ */
+ static UClassID U_EXPORT2 getStaticClassID();
+
+protected:
+
+ /*
+ * Since this class has pure virtual functions,
+ * a constructor can't be used.
+ * @stable ICU 2.0
+ */
+/* UnicodeFilter();*/
+};
+
+/*inline UnicodeFilter::UnicodeFilter() {}*/
+
+U_NAMESPACE_END
+
+#endif