Added a config class to ease passing a set of options across webrtc.
Its main design reason is to expose control of experimental webrtc features.
R=niklas.enbom@webrtc.org
Review URL: https://webrtc-codereview.appspot.com/1450009
git-svn-id: http://webrtc.googlecode.com/svn/trunk/webrtc@4004 4adac7df-926f-26a2-2b94-8c16560cd09d
diff --git a/common.h b/common.h
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+++ b/common.h
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+/*
+ * 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>
+
+namespace webrtc {
+
+// 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() {}
+// };
+//
+// * accessing an option:
+// config.Get<Algo1_CostFunction>().cost(value);
+//
+// * setting an option:
+// struct SqrCost : Algo1_CostFunction {
+// virtual float cost(int x) const { return x*x; }
+// };
+// config.Set<Algo1_CostFunction>(new SqrCost());
+//
+// Note: This class is thread-compatible (like STL containers).
+class Config {
+ public:
+ // Returns the option if set or a default constructed one.
+ // Callers that access options to often are encouraged to cache the result.
+ // Returned references are owned by this.
+ //
+ // Requires std::is_default_constructible<T>
+ template<typename T> const T& Get() const;
+
+ // Set the option, deleting any previous instance of the same.
+ // This instance gets ownership of the newly setted value.
+ template<typename T> void Set(T* value);
+
+ Config() {}
+ ~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;
+ }
+
+ // 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() {
+ static const T def;
+ return def;
+ }
+
+ typedef std::map<OptionIdentifier, BaseOption*> OptionMap;
+ OptionMap options_;
+
+ // 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