blob: 94eb164986f9b717766a68f6c85d4c10b2e1501a [file] [log] [blame]
/*
* Copyright 2012 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.
*/
// Bind() is an overloaded function that converts method calls into function
// objects (aka functors). The method object is captured as a scoped_refptr<> if
// possible, and as a raw pointer otherwise. Any arguments to the method are
// captured by value. The return value of Bind is a stateful, nullary function
// object. Care should be taken about the lifetime of objects captured by
// Bind(); the returned functor knows nothing about the lifetime of a non
// ref-counted method object or any arguments passed by pointer, and calling the
// functor with a destroyed object will surely do bad things.
//
// To prevent the method object from being captured as a scoped_refptr<>, you
// can use Unretained. But this should only be done when absolutely necessary,
// and when the caller knows the extra reference isn't needed.
//
// Example usage:
// struct Foo {
// int Test1() { return 42; }
// int Test2() const { return 52; }
// int Test3(int x) { return x*x; }
// float Test4(int x, float y) { return x + y; }
// };
//
// int main() {
// Foo foo;
// cout << rtc::Bind(&Foo::Test1, &foo)() << endl;
// cout << rtc::Bind(&Foo::Test2, &foo)() << endl;
// cout << rtc::Bind(&Foo::Test3, &foo, 3)() << endl;
// cout << rtc::Bind(&Foo::Test4, &foo, 7, 8.5f)() << endl;
// }
//
// Example usage of ref counted objects:
// struct Bar {
// int AddRef();
// int Release();
//
// void Test() {}
// void BindThis() {
// // The functor passed to AsyncInvoke() will keep this object alive.
// invoker.AsyncInvoke(RTC_FROM_HERE,rtc::Bind(&Bar::Test, this));
// }
// };
//
// int main() {
// rtc::scoped_refptr<Bar> bar = new rtc::RefCountedObject<Bar>();
// auto functor = rtc::Bind(&Bar::Test, bar);
// bar = nullptr;
// // The functor stores an internal scoped_refptr<Bar>, so this is safe.
// functor();
// }
//
#ifndef WEBRTC_BASE_BIND_H_
#define WEBRTC_BASE_BIND_H_
#include <tuple>
#include <type_traits>
#include "webrtc/base/scoped_ref_ptr.h"
#include "webrtc/base/template_util.h"
#define NONAME
namespace rtc {
namespace detail {
// This is needed because the template parameters in Bind can't be resolved
// if they're used both as parameters of the function pointer type and as
// parameters to Bind itself: the function pointer parameters are exact
// matches to the function prototype, but the parameters to bind have
// references stripped. This trick allows the compiler to dictate the Bind
// parameter types rather than deduce them.
template <class T> struct identity { typedef T type; };
// IsRefCounted<T>::value will be true for types that can be used in
// rtc::scoped_refptr<T>, i.e. types that implements nullary functions AddRef()
// and Release(), regardless of their return types. AddRef() and Release() can
// be defined in T or any superclass of T.
template <typename T>
class IsRefCounted {
// This is a complex implementation detail done with SFINAE.
// Define types such that sizeof(Yes) != sizeof(No).
struct Yes { char dummy[1]; };
struct No { char dummy[2]; };
// Define two overloaded template functions with return types of different
// size. This way, we can use sizeof() on the return type to determine which
// function the compiler would have chosen. One function will be preferred
// over the other if it is possible to create it without compiler errors,
// otherwise the compiler will simply remove it, and default to the less
// preferred function.
template <typename R>
static Yes test(R* r, decltype(r->AddRef(), r->Release(), 42));
template <typename C> static No test(...);
public:
// Trick the compiler to tell if it's possible to call AddRef() and Release().
static const bool value = sizeof(test<T>((T*)nullptr, 42)) == sizeof(Yes);
};
// TernaryTypeOperator is a helper class to select a type based on a static bool
// value.
template <bool condition, typename IfTrueT, typename IfFalseT>
struct TernaryTypeOperator {};
template <typename IfTrueT, typename IfFalseT>
struct TernaryTypeOperator<true, IfTrueT, IfFalseT> {
typedef IfTrueT type;
};
template <typename IfTrueT, typename IfFalseT>
struct TernaryTypeOperator<false, IfTrueT, IfFalseT> {
typedef IfFalseT type;
};
// PointerType<T>::type will be scoped_refptr<T> for ref counted types, and T*
// otherwise.
template <class T>
struct PointerType {
typedef typename TernaryTypeOperator<IsRefCounted<T>::value,
scoped_refptr<T>,
T*>::type type;
};
template <typename T>
class UnretainedWrapper {
public:
explicit UnretainedWrapper(T* o) : ptr_(o) {}
T* get() const { return ptr_; }
private:
T* ptr_;
};
} // namespace detail
template <typename T>
static inline detail::UnretainedWrapper<T> Unretained(T* o) {
return detail::UnretainedWrapper<T>(o);
}
template <class ObjectT, class MethodT, class R, typename... Args>
class MethodFunctor {
public:
MethodFunctor(MethodT method, ObjectT* object, Args... args)
: method_(method), object_(object), args_(args...) {}
R operator()() const {
return CallMethod(typename sequence_generator<sizeof...(Args)>::type());
}
private:
// Use sequence_generator (see template_util.h) to expand a MethodFunctor
// with 2 arguments to (std::get<0>(args_), std::get<1>(args_)), for
// instance.
template <int... S>
R CallMethod(sequence<S...>) const {
return (object_->*method_)(std::get<S>(args_)...);
}
MethodT method_;
typename detail::PointerType<ObjectT>::type object_;
typename std::tuple<typename std::remove_reference<Args>::type...> args_;
};
template <class ObjectT, class MethodT, class R, typename... Args>
class UnretainedMethodFunctor {
public:
UnretainedMethodFunctor(MethodT method,
detail::UnretainedWrapper<ObjectT> object,
Args... args)
: method_(method), object_(object.get()), args_(args...) {}
R operator()() const {
return CallMethod(typename sequence_generator<sizeof...(Args)>::type());
}
private:
// Use sequence_generator (see template_util.h) to expand an
// UnretainedMethodFunctor with 2 arguments to (std::get<0>(args_),
// std::get<1>(args_)), for instance.
template <int... S>
R CallMethod(sequence<S...>) const {
return (object_->*method_)(std::get<S>(args_)...);
}
MethodT method_;
ObjectT* object_;
typename std::tuple<typename std::remove_reference<Args>::type...> args_;
};
template <class FunctorT, class R, typename... Args>
class Functor {
public:
Functor(const FunctorT& functor, Args... args)
: functor_(functor), args_(args...) {}
R operator()() const {
return CallFunction(typename sequence_generator<sizeof...(Args)>::type());
}
private:
// Use sequence_generator (see template_util.h) to expand a Functor
// with 2 arguments to (std::get<0>(args_), std::get<1>(args_)), for
// instance.
template <int... S>
R CallFunction(sequence<S...>) const {
return functor_(std::get<S>(args_)...);
}
FunctorT functor_;
typename std::tuple<typename std::remove_reference<Args>::type...> args_;
};
#define FP_T(x) R (ObjectT::*x)(Args...)
template <class ObjectT, class R, typename... Args>
MethodFunctor<ObjectT, FP_T(NONAME), R, Args...> Bind(
FP_T(method),
ObjectT* object,
typename detail::identity<Args>::type... args) {
return MethodFunctor<ObjectT, FP_T(NONAME), R, Args...>(method, object,
args...);
}
template <class ObjectT, class R, typename... Args>
MethodFunctor<ObjectT, FP_T(NONAME), R, Args...> Bind(
FP_T(method),
const scoped_refptr<ObjectT>& object,
typename detail::identity<Args>::type... args) {
return MethodFunctor<ObjectT, FP_T(NONAME), R, Args...>(method, object.get(),
args...);
}
template <class ObjectT, class R, typename... Args>
UnretainedMethodFunctor<ObjectT, FP_T(NONAME), R, Args...> Bind(
FP_T(method),
detail::UnretainedWrapper<ObjectT> object,
typename detail::identity<Args>::type... args) {
return UnretainedMethodFunctor<ObjectT, FP_T(NONAME), R, Args...>(
method, object, args...);
}
#undef FP_T
#define FP_T(x) R (ObjectT::*x)(Args...) const
template <class ObjectT, class R, typename... Args>
MethodFunctor<const ObjectT, FP_T(NONAME), R, Args...> Bind(
FP_T(method),
const ObjectT* object,
typename detail::identity<Args>::type... args) {
return MethodFunctor<const ObjectT, FP_T(NONAME), R, Args...>(method, object,
args...);
}
template <class ObjectT, class R, typename... Args>
UnretainedMethodFunctor<const ObjectT, FP_T(NONAME), R, Args...> Bind(
FP_T(method),
detail::UnretainedWrapper<const ObjectT> object,
typename detail::identity<Args>::type... args) {
return UnretainedMethodFunctor<const ObjectT, FP_T(NONAME), R, Args...>(
method, object, args...);
}
#undef FP_T
#define FP_T(x) R (*x)(Args...)
template <class R, typename... Args>
Functor<FP_T(NONAME), R, Args...> Bind(
FP_T(function),
typename detail::identity<Args>::type... args) {
return Functor<FP_T(NONAME), R, Args...>(function, args...);
}
#undef FP_T
} // namespace rtc
#undef NONAME
#endif // WEBRTC_BASE_BIND_H_