extensions/common/value_counter.h

   1 // Copyright 2014 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef EXTENSIONS_COMMON_VALUE_COUNTER_H_
   6 #define EXTENSIONS_COMMON_VALUE_COUNTER_H_
   7
   8 #include "base/memory/scoped_vector.h"
   9
  10 namespace base {
  11 class Value;
  12 }
  13
  14 namespace extensions {
  15
  16 // Keeps a running count of Values, like map<Value, int>. Adding/removing
  17 // values increments/decrements the count associated with a given Value.
  18 //
  19 // Add() and Remove() are linear in the number of Values in the ValueCounter,
  20 // because there is no operator<() defined on Value, so we must iterate to find
  21 // whether a Value is equal to an existing one.
  22 class ValueCounter {
  23  public:
  24   ValueCounter();
  25   ~ValueCounter();
  26
  27   // Adds |value| to the set. In the case where a Value equal to |value|
  28   // doesn't already exist in this map, this function makes a copy of |value|
  29   // and returns true. Otherwise, it returns false.
  30   bool Add(const base::Value& value);
  31
  32   // Removes |value| from the set, and returns true if it removed the last
  33   // value equal to |value|. If there are more equal values, or if there
  34   // weren't any in the first place, returns false.
  35   bool Remove(const base::Value& value);
  36
  37   // Returns true if there are no values of any type being counted.
  38   bool is_empty() const { return entries_.empty(); }
  39
  40  private:
  41   struct Entry;
  42   ScopedVector<Entry> entries_;
  43
  44   DISALLOW_COPY_AND_ASSIGN(ValueCounter);
  45 };
  46
  47 }  // namespace extensions
  48
  49 #endif  // EXTENSIONS_COMMON_VALUE_COUNTER_H_