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/*
* 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.
*/
// To generate callback.h from callback.h.pump, execute:
// /home/build/google3/third_party/gtest/scripts/pump.py callback.h.pump
// Callbacks are callable object containers. They can hold a function pointer
// or a function object and behave like a value type. Internally, data is
// reference-counted, making copies and pass-by-value inexpensive.
//
// Callbacks are typed using template arguments. The format is:
// CallbackN<ReturnType, ParamType1, ..., ParamTypeN>
// where N is the number of arguments supplied to the callable object.
// Callbacks are invoked using operator(), just like a function or a function
// object. Default-constructed callbacks are "empty," and executing an empty
// callback does nothing. A callback can be made empty by assigning it from
// a default-constructed callback.
//
// Callbacks are similar in purpose to std::function (which isn't available on
// all platforms we support) and a lightweight alternative to sigslots. Since
// they effectively hide the type of the object they call, they're useful in
// breaking dependencies between objects that need to interact with one another.
// Notably, they can hold the results of Bind(), std::bind*, etc, without needing
// to know the resulting object type of those calls.
//
// Sigslots, on the other hand, provide a fuller feature set, such as multiple
// subscriptions to a signal, optional thread-safety, and lifetime tracking of
// slots. When these features are needed, choose sigslots.
//
// Example:
// int sqr(int x) { return x * x; }
// struct AddK {
// int k;
// int operator()(int x) const { return x + k; }
// } add_k = {5};
//
// Callback1<int, int> my_callback;
// cout << my_callback.empty() << endl; // true
//
// my_callback = Callback1<int, int>(&sqr);
// cout << my_callback.empty() << endl; // false
// cout << my_callback(3) << endl; // 9
//
// my_callback = Callback1<int, int>(add_k);
// cout << my_callback(10) << endl; // 15
//
// my_callback = Callback1<int, int>();
// cout << my_callback.empty() << endl; // true
#ifndef WEBRTC_BASE_CALLBACK_H_
#define WEBRTC_BASE_CALLBACK_H_
#include "webrtc/base/refcount.h"
#include "webrtc/base/scoped_ref_ptr.h"
namespace rtc {
$var n = 5
$range i 0..n
$for i [[
$range j 1..i
template <class R$for j [[,
class P$j]]>
class Callback$i {
public:
// Default copy operations are appropriate for this class.
Callback$i() {}
template <class T> Callback$i(const T& functor)
: helper_(new RefCountedObject< HelperImpl<T> >(functor)) {}
R operator()($for j , [[P$j p$j]]) {
if (empty())
return R();
return helper_->Run($for j , [[p$j]]);
}
bool empty() const { return !helper_; }
private:
struct Helper : RefCountInterface {
virtual ~Helper() {}
virtual R Run($for j , [[P$j p$j]]) = 0;
};
template <class T> struct HelperImpl : Helper {
explicit HelperImpl(const T& functor) : functor_(functor) {}
virtual R Run($for j , [[P$j p$j]]) {
return functor_($for j , [[p$j]]);
}
T functor_;
};
scoped_refptr<Helper> helper_;
};
]]
} // namespace rtc
#endif // WEBRTC_BASE_CALLBACK_H_
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