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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 too 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 set 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_
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