Issue 5141 - Generalize Map class to allow non-strings as keys

compiled/StringMap.h

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
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  * it under the terms of the GNU General Public License version 3 as
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  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  * GNU General Public License for more details.
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  * along with Adblock Plus.  If not, see <http://www.gnu.org/licenses/>.
  */
 
 #pragma once
 
 #include <cstddef>
 
 #include "Map.h"
 #include "String.h"
 
 namespace StringMap_internal
 {
   struct StringSetEntry
   {
-    typedef String key_type;
+    typedef DependentString key_type;
+    typedef const String& key_type_cref;
     typedef size_t size_type;
 
-    DependentString first;

[sergei, 2017/10/17 12:58:06]

Actually, the type of `first` should be key_type, thus key_type should be
DependentString. What do you think about having
typedef const String& key_type_cref;
and using it everywhere as the argument type? It seems it also solves
https://codereview.adblockplus.org/29572731/diff/29572868/compiled/IntMap.h#n....

[Wladimir Palant, 2017/12/04 13:44:15]

Done.

+    key_type first;
 
-    StringSetEntry(const key_type& key = DependentString())
+    StringSetEntry(key_type_cref key = key_type())
     {
       if (!key.is_invalid())
         first.reset(key);

[sergei, 2017/10/17 12:58:06]

Why is this trick required and `:first(key)` cannot be used?
I have actually tried it with the current key_type and the compiler hangs up.

[Wladimir Palant, 2017/12/04 13:44:15]

That's because DepedentString() constructor will create a valid empty string if
constructed from an invalid DependentString() instance. Having DependentString()
constructor copy flags isn't entirely trivial however.

[sergei, 2017/12/04 14:26:09]

I have added a ticket for that because it seems a serious issue which has been
already observed in several places. https://issues.adblockplus.org/ticket/6138.

     }
 
-    bool equals(const key_type& other) const
+    bool equals(key_type_cref other) const
     {
       return first.equals(other);
     }
 
     bool is_invalid() const
     {
       return first.is_invalid();
     }
 
     bool is_deleted() const
     {
       return first.is_deleted();
     }
 
     void erase()
     {
       first.erase();
     }
 
-    static size_type hash(const key_type& key)
+    static size_type hash(key_type_cref key)
     {
       // FNV-1a hash function
       size_type result = 2166136261;
       for (String::size_type i = 0; i < key.length(); i++)
         result = (result ^ key[i]) * 16777619;
       return result;
     }
   };
 
   template<typename Value>
   struct StringMapEntry : StringSetEntry
   {
     typedef StringSetEntry super;
     typedef Value value_type;
 
-    Value second;
+    value_type second;
 
-    StringMapEntry(const key_type& key = DependentString(),
+    StringMapEntry(key_type_cref key = DependentString(),
                    value_type value = value_type())
         : super(key), second(value)
     {
     }
 
     void erase()
     {
       super::erase();
       second = value_type();
     }
   };
 }
 
 using StringSet = Set<StringMap_internal::StringSetEntry>;
 
 template<typename Value>
 using StringMap = Map<StringMap_internal::StringMapEntry<Value>>;