[Courgette] Initial Implementation of LabelManager.

courgette/consecutive_range_visitor.h

Index: courgette/consecutive_range_visitor.h
diff --git a/courgette/consecutive_range_visitor.h b/courgette/consecutive_range_visitor.h
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+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_
+#define COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_
+
+#include <iterator>
+
+#include "base/macros.h"
+
+namespace courgette {
+
+// Usage note: First check whether std::unique() would suffice.
+//
+// ConsecutiveRangeVisitor is a visitor to read equal consecutive items
+// ("ranges") between two iterators. The base value of InputIterator must
+// implement the == operator.
+//
+// Example: "AAAAABZZZZOO" consists of ranges ["AAAAA", "B", "ZZZZ", "OO"]. The
+// visitor provides accessors to iterate through the ranges, and to access each
+// range's value and repeat, i.e., [('A', 5), ('B', 1), ('Z', 4), ('O', 2)].
+template <class InputIterator>
+class ConsecutiveRangeVisitor {
+ public:
+  ConsecutiveRangeVisitor(InputIterator begin, InputIterator end)
+      : head_(begin), end_(end) {
+    advance();
+  }
+
+  // Returns whether there are more ranges to traverse.
+  bool has_more() const { return tail_ != end_; }
+
+  // Returns an iterator to an element in the current range.
+  InputIterator cur() const { return tail_; }
+
+  // Returns the number of repeated elements in the current range.
+  size_t repeat() const { return std::distance(tail_, head_); }
+
+  // Advances to the next range.
+  void advance() {
+    tail_ = head_;
+    if (head_ != end_)
+      while (++head_ != end_ && *head_ == *tail_) {}
+  }
+
+ private:
+  InputIterator tail_;  // The trailing pionter of a range (inclusive).
+  InputIterator head_;  // The leading pointer of a range (exclusive).
+  InputIterator end_;   // Store the end pointer so we know when to stop.
+
+  DISALLOW_COPY_AND_ASSIGN(ConsecutiveRangeVisitor);
+};
+
+}  // namespace courgette
+
+#endif  // COURGETTE_CONSECUTIVE_RANGE_VISITOR_H_