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+/*
+ * Copyright (C) 2010, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1.  Redistributions of source code must retain the above copyright
+ *     notice, this list of conditions and the following disclaimer.
+ * 2.  Redistributions in binary form must reproduce the above copyright
+ *     notice, this list of conditions and the following disclaimer in the
+ *     documentation and/or other materials provided with the distribution.
+ *
+ * THIS SOFTWARE IS PROVIDED BY APPLE INC. AND ITS CONTRIBUTORS ``AS IS'' AND ANY
+ * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+ * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+ * DISCLAIMED. IN NO EVENT SHALL APPLE INC. OR ITS CONTRIBUTORS BE LIABLE FOR ANY
+ * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+ * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+ * LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ * ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+ * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#ifndef TextPosition_h
+#define TextPosition_h
+
+#include <wtf/Assertions.h>
+
+namespace WTF {
+
+/*
+ * Text Position
+ *
+ * TextPosition structure specifies coordinates within an text resource. It is used mostly
+ * for saving script source position.
+ *
+ * Later TextPosition0 and TextPosition1 and both number types can be merged together quite easily.
+ *
+ * 0-based and 1-based
+ *
+ * Line and column numbers could be interpreted as zero-based or 1-based. Since
+ * both practices coexist in WebKit source base, 'int' type should be replaced with
+ * a dedicated wrapper types, so that compiler helped us with this ambiguity.
+ *
+ * Here we introduce 2 types of numbers: ZeroBasedNumber and OneBasedNumber and
+ * 2 corresponding types of TextPosition structure. While only one type ought to be enough,
+ * this is done to keep transition to the new types as transparent as possible:
+ * e.g. in areas where 0-based integers are used, TextPosition0 should be introduced. This
+ * way all changes will remain trackable.
+ *
+ * Later both number types can be merged in one type quite easily.
+ *
+ * For type safety and for the future type merge it is important that all operations in API
+ * that accept or return integer have a name explicitly defining base of integer. For this reason
+ * int-receiving constructors are hidden from API.
+ */
+
+template<typename NUMBER>
+class TextPosition {
+public:
+    TextPosition(NUMBER line, NUMBER column)
+        : m_line(line)
+        , m_column(column)
+    {
+    }
+    TextPosition() {}
+
+    bool operator==(const TextPosition& other) { return m_line == other.m_line && m_column == other.m_column; }
+    bool operator!=(const TextPosition& other) { return !((*this) == other); }
+
+    // A 'minimum' value of position, used as a default value.
+    static TextPosition<NUMBER> minimumPosition() { return TextPosition<NUMBER>(NUMBER::base(), NUMBER::base()); }
+
+    // A value with line value less than a minimum; used as an impossible position.
+    static TextPosition<NUMBER> belowRangePosition() { return TextPosition<NUMBER>(NUMBER::belowBase(), NUMBER::belowBase()); }
+
+    NUMBER m_line;
+    NUMBER m_column;
+};
+
+class OneBasedNumber;
+
+// An int wrapper that always reminds you that the number should be 0-based
+class ZeroBasedNumber {
+public:
+    static ZeroBasedNumber fromZeroBasedInt(int zeroBasedInt) { return ZeroBasedNumber(zeroBasedInt); }
+
+    ZeroBasedNumber() {}
+
+    int zeroBasedInt() const { return m_value; }
+
+    OneBasedNumber convertToOneBased() const;
+
+    bool operator==(ZeroBasedNumber other) { return m_value == other.m_value; }
+    bool operator!=(ZeroBasedNumber other) { return !((*this) == other); }
+
+    static ZeroBasedNumber base() { return 0; }
+    static ZeroBasedNumber belowBase() { return -1; }
+
+private:
+    ZeroBasedNumber(int value) : m_value(value) {}
+    int m_value;
+};
+
+// An int wrapper that always reminds you that the number should be 1-based
+class OneBasedNumber {
+public:
+    static OneBasedNumber fromOneBasedInt(int oneBasedInt) { return OneBasedNumber(oneBasedInt); }
+    OneBasedNumber() {}
+
+    int oneBasedInt() const { return m_value; }
+    int convertAsZeroBasedInt() const { return m_value - 1; }
+    ZeroBasedNumber convertToZeroBased() const { return ZeroBasedNumber::fromZeroBasedInt(m_value - 1); }
+
+    bool operator==(OneBasedNumber other) { return m_value == other.m_value; }
+    bool operator!=(OneBasedNumber other) { return !((*this) == other); }
+
+    static OneBasedNumber base() { return 1; }
+    static OneBasedNumber belowBase() { return 0; }
+
+private:
+    OneBasedNumber(int value) : m_value(value) {}
+    int m_value;
+};
+
+typedef TextPosition<ZeroBasedNumber> TextPosition0;
+typedef TextPosition<OneBasedNumber> TextPosition1;
+
+inline TextPosition0 toZeroBasedTextPosition(const TextPosition1& position)
+{
+    return TextPosition0(position.m_line.convertToZeroBased(), position.m_column.convertToZeroBased());
+}
+
+inline TextPosition1 toOneBasedTextPosition(const TextPosition0& position)
+{
+    return TextPosition1(position.m_line.convertToOneBased(), position.m_column.convertToOneBased());
+}
+
+inline OneBasedNumber ZeroBasedNumber::convertToOneBased() const
+{
+    return OneBasedNumber::fromOneBasedInt(m_value + 1);
+}
+
+}
+
+using WTF::TextPosition0;
+using WTF::TextPosition1;
+
+#endif // TextPosition_h