base: Remove non-const refs from the MRUCache implementation.

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.
@@ skipping 122 matching lines @@
   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;
   }
 
   // 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);
+    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).
   reverse_iterator Erase(reverse_iterator pos) {
     // We have to actually give it the incremented iterator to delete, since
     // the forward iterator that base() returns is actually one past the item
     // being iterated over.
     return reverse_iterator(Erase((++pos).base()));
   }
 
   // Shrinks the cache so it only holds |new_size| items. If |new_size| is
   // bigger or equal to the current number of items, this will do nothing.
   void ShrinkToSize(size_type new_size) {
     for (size_type i = size(); i > new_size; i--)
       Erase(rbegin());
   }
 
   // Deletes everything from the cache.
   void Clear() {
     for (typename PayloadList::iterator i(ordering_.begin());
          i != ordering_.end(); ++i)
-      deletor_(i->second);
+      deletor_(&i->second);
     index_.clear();
     ordering_.clear();
   }
 
   // Returns the number of elements in the cache.
   size_type size() const {
     // We don't use ordering_.size() for the return value because
     // (as a linked list) it can be O(n).
     DCHECK(index_.size() == ordering_.size());
     return index_.size();
@@ skipping 27 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(MRUCacheBase);
 };
 
 // MRUCache --------------------------------------------------------------------
 
 // A functor that does nothing. Used by the MRUCache.
 template<class PayloadType>
 class MRUCacheNullDeletor {
  public:
-  void operator()(PayloadType& payload) {
-  }
+  void operator()(PayloadType* payload) {}
 };
 
 // A container that does not do anything to free its data. Use this when storing
 // value types (as opposed to pointers) in the list.
 template <class KeyType, class PayloadType>
 class MRUCache : public MRUCacheBase<KeyType,
                                      PayloadType,
                                      MRUCacheNullDeletor<PayloadType> > {
  private:
   typedef MRUCacheBase<KeyType, PayloadType,
       MRUCacheNullDeletor<PayloadType> > ParentType;
 
  public:
   // See MRUCacheBase, noting the possibility of using NO_AUTO_EVICT.
   explicit MRUCache(typename ParentType::size_type max_size)
       : ParentType(max_size) {
   }
   virtual ~MRUCache() {
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(MRUCache);
 };
 
 // OwningMRUCache --------------------------------------------------------------
 
 template<class PayloadType>
 class MRUCachePointerDeletor {
  public:
-  void operator()(PayloadType& payload) {
-    delete payload;
-  }
+  void operator()(PayloadType* payload) { delete *payload; }

[Nico, 2015/03/07 01:06:14]

can't you just make this const PalyloadType& ? I think deleting const refs
should be ok?

 };
 
 // A cache that owns the payload type, which must be a non-const pointer type.
 // The pointers will be deleted when they are removed, replaced, or when the
 // cache is destroyed.
 template <class KeyType, class PayloadType>
 class OwningMRUCache
     : public MRUCacheBase<KeyType,
                           PayloadType,
                           MRUCachePointerDeletor<PayloadType> > {
@@ skipping 41 matching lines @@
   virtual ~HashingMRUCache() {
   }
 
  private:
   DISALLOW_COPY_AND_ASSIGN(HashingMRUCache);
 };
 
 }  // namespace base
 
 #endif  // BASE_CONTAINERS_MRU_CACHE_H_