I'm trying to learn some basic c++11 concepts by implementing some well known design patterns. Currently I'm stuck at Callables while trying to implement the new Angular2 EventEmitter Pattern in C++. So here is the code if the comment stays all is ok:
class Controller {
public:
Controller() {
const pattern::EventEmitter<SwitchEvent> listner;
listner.subscribe([this](const SwitchEvent& event) {
if(event.get_state()) {
this->_count++;
std::cout << "count: " << this->_count << std::endl;
}
});
//listner.subscribe(std::bind(&Controller::track, this));
}
private:
int _count = 0;
void track(const SwitchEvent& event) {
if(!event.get_state()) {
this->_count++;
std::cout << "count: " << this->_count << std::endl;
}
}
};
and the output is as expected:
$ g++ -std=c++11 -Wall test.cc
$ ./a.out
count: 1
But when I remove the comment I get an Error:
test.cc: In constructor ‘Controller::Controller()’:
test.cc:50:62: error: no matching function for call to ‘pattern::EventEmitter<SwitchEvent>::subscribe(std::_Bind_helper<false, void (Controller::*)(const SwitchEvent&), Controller*>::type) const’
listner.subscribe(std::bind(&Controller::track, this));
^
test.cc:50:62: note: candidate is:
In file included from test.cc:1:0:
EventEmitter.hh:16:6: note: void pattern::EventEmitter<T>::subscribe(const std::function<void(const T&)>&) const [with T = SwitchEvent]
void subscribe(const std::function<void(const T&)>& listener) const {
^
EventEmitter.hh:16:6: note: no known conversion for argument 1 from ‘std::_Bind_helper<false, void (Controller::*)(const SwitchEvent&), Controller*>::type {aka std::_Bind<std::_Mem_fn<void (Controller::*)(const SwitchEvent&)>(Controller*)>}’ to ‘const std::function<void(const SwitchEvent&)>&’
You need to provide bind
a placeholder so it knows that it takes an argument:
listner.subscribe(std::bind(&Controller::track, this, std::placeholders::_1));
Otherwise, it will give you a nullary function object, which you cannot construct your std::function
with.
You need to pass through the "second" argument to track()
, which is the event. The first argument you bind to this
, but the second is missing. So you need something like this:
using namespace std::placeholders;
listner.subscribe(std::bind(&Controller::track, this, _1));
Since you tagged it as C++11 then you would be better of using a lambda:
listner.subscribe([this](const SwitchEvent& event) {
if(!event.get_state()) {
_count++;
std::cout << "count: " << _count << std::endl;
}});
Otherwise use a placeholder for the track parameter, event
:
listner.subscribe(std::bind(&Controller::track, this, std::placeholders::_1));
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