Re-land: "Use an explicit identifier in Config"

webrtc/common.h

 /*
  *  Copyright (c) 2013 The WebRTC project authors. All Rights Reserved.
  *
  *  Use of this source code is governed by a BSD-style license
  *  that can be found in the LICENSE file in the root of the source
  *  tree. An additional intellectual property rights grant can be found
  *  in the file PATENTS.  All contributing project authors may
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
 #ifndef WEBRTC_COMMON_H_
 #define WEBRTC_COMMON_H_
 
 #include <map>
 
 #include "webrtc/base/basictypes.h"
 
 namespace webrtc {
 
+// Only add new values to the end of the enumeration and never remove (only
+// deprecate) to maintain binary compatibility.
+enum class ConfigOptionID {
+  kMyExperimentForTest,
+  kAlgo1CostFunctionForTest,
+  kTemporalLayersFactory,
+  kNetEqCapacityConfig,
+  kNetEqFastAccelerate,
+  kVoicePacing,
+  kExtendedFilter,
+  kDelayAgnostic,
+  kExperimentalAgc,
+  kExperimentalNs,
+  kBeamforming,
+  kIntelligibility
+};
+
 // Class Config is designed to ease passing a set of options across webrtc code.
 // Options are identified by typename in order to avoid incorrect casts.
 //
 // Usage:
 // * declaring an option:
 //    struct Algo1_CostFunction {
 //      virtual float cost(int x) const { return x; }
 //      virtual ~Algo1_CostFunction() {}
 //    };
 //
@@ skipping 24 matching lines @@
   ~Config() {
     // Note: this method is inline so webrtc public API depends only
     // on the headers.
     for (OptionMap::iterator it = options_.begin();
          it != options_.end(); ++it) {
       delete it->second;
     }
   }
 
  private:
-  typedef void* OptionIdentifier;
-
   struct BaseOption {
     virtual ~BaseOption() {}
   };
 
   template<typename T>
   struct Option : BaseOption {
     explicit Option(T* v): value(v) {}
     ~Option() {
       delete value;
     }
     T* value;
   };
 
-  // Own implementation of rtti-subset to avoid depending on rtti and its costs.
   template<typename T>
-  static OptionIdentifier identifier() {
-    static char id_placeholder;
-    return &id_placeholder;
+  static ConfigOptionID identifier() {
+    return T::identifier;
   }
 
   // Used to instantiate a default constructed object that doesn't needs to be
   // owned. This allows Get<T> to be implemented without requiring explicitly
   // locks.
   template<typename T>
   static const T& default_value() {
     RTC_DEFINE_STATIC_LOCAL(const T, def, ());
     return def;
   }
 
-  typedef std::map<OptionIdentifier, BaseOption*> OptionMap;
+  typedef std::map<ConfigOptionID, BaseOption*> OptionMap;
   OptionMap options_;
 
   // RTC_DISALLOW_COPY_AND_ASSIGN
   Config(const Config&);
   void operator=(const Config&);
 };
 
 template<typename T>
 const T& Config::Get() const {
   OptionMap::const_iterator it = options_.find(identifier<T>());
   if (it != options_.end()) {
     const T* t = static_cast<Option<T>*>(it->second)->value;
     if (t) {
       return *t;
     }
   }
   return default_value<T>();
 }
 
 template<typename T>
 void Config::Set(T* value) {
   BaseOption*& it = options_[identifier<T>()];
   delete it;
   it = new Option<T>(value);
 }
 
 }  // namespace webrtc
 
 #endif  // WEBRTC_COMMON_H_