MRUCacheBase - Added Swap method to exchange contents of two MRUCache

base/containers/mru_cache.h

 // Copyright (c) 2011 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.
 
 // This file contains a template for a Most Recently Used cache that allows
 // constant-time access to items using a key, but easy identification of the
 // least-recently-used items for removal.  Each key can only be associated with
 // one payload item at a time.
 //
 // The key object will be stored twice, so it should support efficient copying.
 //
 // NOTE: While all operations are O(1), this code is written for
 // legibility rather than optimality. If future profiling identifies this as
 // a bottleneck, there is room for smaller values of 1 in the O(1). :]
 
 #ifndef BASE_CONTAINERS_MRU_CACHE_H_
 #define BASE_CONTAINERS_MRU_CACHE_H_
 
+#include <algorithm>
 #include <list>
 #include <map>
 #include <utility>
 
 #include "base/basictypes.h"
 #include "base/containers/hash_tables.h"
 #include "base/logging.h"
 
 namespace base {
 
@@ skipping 101 matching lines @@
     return index_iter->second;
   }
 
   const_iterator Peek(const KeyType& key) const {
     typename KeyIndex::const_iterator index_iter = index_.find(key);
     if (index_iter == index_.end())
       return end();
     return index_iter->second;
   }
 
+  // Exchanges the contents of |this| by the contents of the |other|.
+  void Swap(MRUCacheBase& other) {
+    ordering_.swap(other.ordering_);
+    index_.swap(other.index_);
+    std::swap(deletor_, other.deletor_);
+    std::swap(max_size_, other.max_size_);
+  }
+
   // Erases the item referenced by the given iterator. An iterator to the item
   // following it will be returned. The iterator must be valid.
   iterator Erase(iterator pos) {
     deletor_(pos->second);
     index_.erase(pos->first);
     return ordering_.erase(pos);
   }
 
   // MRUCache entries are often processed in reverse order, so we add this
   // convenience function (not typically defined by STL containers).
@@ skipping 148 matching lines @@
   virtual ~HashingMRUCache() {
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HashingMRUCache);
 };
 
 }  // namespace base
 
 #endif  // BASE_CONTAINERS_MRU_CACHE_H_