std::bind() error: cannot determine which instance of overloaded function "boost::asio::io_service::run" is intended

Question

While trying to compile this in Visual C++ 2015

  auto worker = std::bind(&boost::asio::io_service::run, &(this->service));

I'm getting errors:

error C2783: 'std::_Binder<_Ret,_Fx,_Types...> std::bind(_Fx &&,_Types &&...)': could not deduce template argument for '_Ret'
note: see declaration of 'std::bind'

error C2783: 'std::_Binder<_Ret,_Fx,_Types...> std::bind(_Fx &&,_Types &&...)': could not deduce template argument for '_Fx'
note: see declaration of 'std::bind'

error C2783: 'std::_Binder<std::_Unforced,_Fx,_Types...> std::bind(_Fx &&,_Types &&...)': could not deduce template argument for '_Fx'
note: see declaration of 'std::bind'

Additionally, IntelliSense complains with:

cannot determine which instance of overloaded function "boost::asio::io_service::run" is intended

I see that there are 2 overloads of boost::asio::io_service::run. But how can I specify which one to use?

With boost::bind the code compiles just fine:

  auto worker = boost::bind(&boost::asio::io_service::run, &(this->service));

Answer 1

Since boost::asio::io_service::run has two overloads, you need to specify which to use when using it as a function pointer⁽¹⁾. This needs to be done by casting it to the right function signature:

static_cast<std::size_t(boost::asio::io_service::*)()>(&boost::asio::io_service::run)

Since this looks horrible, I suggest to use a lambda instead of the bind expression. Inside a lambda, the normal overload resolution takes place, so you don't need to specify the overload explicitly:

auto worker = [this]{ return service.run(); };

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^{(1) The problem is that std::bind takes the function by an unrestricted template argument, so the rules of template type deduction apply instead of overload resolution. C++ can't determine what the type of _Fx should be here, since you pass something whose type is not specified. Even if there was a trick such that C++ can try to resolve the overload when using the fact that the bound arguments are going to be passed to the function, note that actually both overloads are possible here: The overload with boost::system::error_code & ec would simply be not bound and "curried" instead (specifying the value for that parameter is delayed to the point when worker is called).}