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 <vector>
   9
  10 #include "base/memory/linked_ptr.h"
  11
  12 namespace base {
  13 class Value;
  14 }
  15
  16 namespace extensions {
  17
  18 // Keeps a running count of Values, like map<Value, int>. Adding / removing
  19 // values increments / decrements the count associated with a given Value.
  20 //
  21 // Add() and Remove() are linear in the number of Values in the ValueCounter,
  22 // because there is no operator<() defined on Value, so we must iterate to find
  23 // whether a Value is equal to an existing one.
  24 class ValueCounter {
  25  public:
  26   ValueCounter();
  27   ~ValueCounter();
  28
  29   // Adds |value| to the set and returns how many equal values are in the set
  30   // after. Does not take ownership of |value|. In the case where a Value equal
  31   // to |value| doesn't already exist in this map, this function makes a
  32   // DeepCopy() of |value|.
  33   int Add(const base::Value& value);
  34
  35   // Removes |value| from the set and returns how many equal values are in
  36   // the set after.
  37   int Remove(const base::Value& value);
  38
  39   // Same as Add() but only performs the add if the value isn't present.
  40   int AddIfMissing(const base::Value& value);
  41
  42  private:
  43   class Entry {
  44    public:
  45     explicit Entry(const base::Value& value);
  46     ~Entry();
  47
  48     int Increment();
  49     int Decrement();
  50
  51     const base::Value* value() const { return value_.get(); }
  52     int count() const { return count_; }
  53
  54    private:
  55     linked_ptr<base::Value> value_;
  56     int count_;
  57
  58     DISALLOW_COPY_AND_ASSIGN(Entry);
  59   };
  60   typedef std::vector<linked_ptr<Entry> > EntryList;
  61
  62   int AddImpl(const base::Value& value, bool increment);
  63
  64   EntryList entries_;
  65
  66   DISALLOW_COPY_AND_ASSIGN(ValueCounter);
  67 };
  68
  69 }  // namespace extensions
  70
  71 #endif  // EXTENSIONS_COMMON_VALUE_COUNTER_H_