i'm sure this must be an common issue so apologies if it's just my search skills that are failing.
i'm trying to do this without boost because the functionality exists in C++11 and i'm a fan of standards.
i'm trying to use std::bind() to wrap a method in a class from an external library. (specifically: asio::io_service::run() ) unfortunately the method is overloaded which confuses std::bind().
minimal test case to demonstrate the issue:
#include <functional> // std::bind
class Test{
public:
void method(){}
void method(int i){}
};
int main(int argc, char * argv[]) {
Test test_instance;
auto bound_thing_1 = std::bind(Test::method, test_instance);
return 0;
}
and compile:
duncan@casper:/tmp/bind_test$ gcc -v
Using built-in specs.
COLLECT_GCC=gcc
COLLECT_LTO_WRAPPER=/usr/lib/gcc/x86_64-linux-gnu/5/lto-wrapper
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 5.3.1-14ubuntu2.1' --with-bugurl=file:///usr/share/doc/gcc-5/README.Bugs --enable-languages=c,ada,c++,java,go,d,fortran,objc,obj-c++ --prefix=/usr --program-suffix=-5 --enable-shared --enable-linker-build-id --libexecdir=/usr/lib --without-included-gettext --enable-threads=posix --libdir=/usr/lib --enable-nls --with-sysroot=/ --enable-clocale=gnu --enable-libstdcxx-debug --enable-libstdcxx-time=yes --with-default-libstdcxx-abi=new --enable-gnu-unique-object --disable-vtable-verify --enable-libmpx --enable-plugin --with-system-zlib --disable-browser-plugin --enable-java-awt=gtk --enable-gtk-cairo --with-java-home=/usr/lib/jvm/java-1.5.0-gcj-5-amd64/jre --enable-java-home --with-jvm-root-dir=/usr/lib/jvm/java-1.5.0-gcj-5-amd64 --with-jvm-jar-dir=/usr/lib/jvm-exports/java-1.5.0-gcj-5-amd64 --with-arch-directory=amd64 --with-ecj-jar=/usr/share/java/eclipse-ecj.jar --enable-objc-gc --enable-multiarch --disable-werror --with-arch-32=i686 --with-abi=m64 --with-multilib-list=m32,m64,mx32 --enable-multilib --with-tune=generic --enable-checking=release --build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 5.3.1 20160413 (Ubuntu 5.3.1-14ubuntu2.1)
duncan@casper:/tmp/bind_test$ /usr/bin/g++ -Wall -std=c++11 ./main.c -o test.bin
./main.c: In function ‘int main(int, char**)’:
./main.c:12:61: error: no matching function for call to ‘bind(<unresolved overloaded function type>, Test&)’
auto bound_thing_1 = std::bind(Test::method, test_instance);
^
In file included from /usr/include/c++/5/memory:79:0,
from /usr/include/asio/detail/addressof.hpp:21,
from /usr/include/asio/detail/handler_alloc_helpers.hpp:19,
from /usr/include/asio/detail/bind_handler.hpp:19,
from /usr/include/asio/detail/wrapped_handler.hpp:18,
from /usr/include/asio/io_service.hpp:24,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/c++/5/functional:1462:5: note: candidate: template<class _Func, class ... _BoundArgs> typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type std::bind(_Func&&, _BoundArgs&& ...)
bind(_Func&& __f, _BoundArgs&&... __args)
^
/usr/include/c++/5/functional:1462:5: note: template argument deduction/substitution failed:
./main.c:12:61: note: couldn't deduce template parameter ‘_Func’
auto bound_thing_1 = std::bind(Test::method, test_instance);
^
In file included from /usr/include/c++/5/memory:79:0,
from /usr/include/asio/detail/addressof.hpp:21,
from /usr/include/asio/detail/handler_alloc_helpers.hpp:19,
from /usr/include/asio/detail/bind_handler.hpp:19,
from /usr/include/asio/detail/wrapped_handler.hpp:18,
from /usr/include/asio/io_service.hpp:24,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/c++/5/functional:1490:5: note: candidate: template<class _Result, class _Func, class ... _BoundArgs> typename std::_Bindres_helper<_Result, _Func, _BoundArgs>::type std::bind(_Func&&, _BoundArgs&& ...)
bind(_Func&& __f, _BoundArgs&&... __args)
^
/usr/include/c++/5/functional:1490:5: note: template argument deduction/substitution failed:
./main.c:12:61: note: couldn't deduce template parameter ‘_Result’
auto bound_thing_1 = std::bind(Test::method, test_instance);
so the problem there (as i interpret it) is that std::bind does not know whether to use method() or method(int).
my next step was to explicitly tell std::bind() which method:
#include <functional> // std::bind
class Test{
public:
void method(){}
void method(int i){}
};
int main(int argc, char * argv[]) {
Test test_instance;
// auto bound_thing_1 = std::bind(Test::method, test_instance);
auto bound_thing_2 = std::bind(static_cast<void(Test::*)(void)>(&Test::method), test_instance);
return 0;
}
this builds correctly. (yay!)
so now i try to apply the same logic using my desired library: http://think-async.com/Asio/asio-1.10.6/doc/asio/reference/io_service/run.html
#include <asio.hpp>
#include <thread> // std::thread
#include <functional> // std::bind
int main(int argc, char * argv[]) {
asio::io_service io_service_instance;
auto bound_thing_3 = std::bind(static_cast<std::size_t(asio::io_service::*)(void)>(&asio::io_service::run), io_service_instance);
std::thread mythread(bound_thing_3)
return 0;
}
and the compile fails:
duncan@casper:/tmp/bind_test$ /usr/bin/g++ -Wall -std=c++11 ./main.c -o test.bin -lpthread
In file included from /usr/include/c++/5/functional:55:0,
from /usr/include/c++/5/memory:79,
from /usr/include/asio/detail/addressof.hpp:21,
from /usr/include/asio/detail/handler_alloc_helpers.hpp:19,
from /usr/include/asio/detail/bind_handler.hpp:19,
from /usr/include/asio/detail/wrapped_handler.hpp:18,
from /usr/include/asio/io_service.hpp:24,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/c++/5/tuple: In instantiation of ‘constexpr std::_Head_base<_Idx, _Head, false>::_Head_base(_UHead&&) [with _UHead = asio::io_service; long unsigned int _Idx = 0ul; _Head = asio::io_service]’:
/usr/include/c++/5/tuple:369:49: required from ‘constexpr std::_Tuple_impl<_Idx, _Head>::_Tuple_impl(std::_Tuple_impl<_Idx, _Head>&&) [with long unsigned int _Idx = 0ul; _Head = asio::io_service]’
/usr/include/c++/5/tuple:484:17: required from ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(std::_Bind<_Functor(_Bound_args ...)>&&) [with _Functor = std::_Mem_fn<long unsigned int (asio::io_service::*)()>; _Bound_args = {asio::io_service}]’
./main.c:16:130: required from here
/usr/include/c++/5/tuple:115:42: error: use of deleted function ‘asio::io_service::io_service(const asio::io_service&)’
: _M_head_impl(std::forward<_UHead>(__h)) { }
^
In file included from /usr/include/asio/basic_io_object.hpp:19:0,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/io_service.hpp:184:7: note: ‘asio::io_service::io_service(const asio::io_service&)’ is implicitly deleted because the default definition would be ill-formed:
class io_service
^
In file included from /usr/include/asio/io_service.hpp:23:0,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/detail/noncopyable.hpp:31:3: error: ‘asio::detail::noncopyable::noncopyable(const asio::detail::noncopyable&)’ is private
noncopyable(const noncopyable&);
^
In file included from /usr/include/asio/basic_io_object.hpp:19:0,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/io_service.hpp:184:7: error: within this context
class io_service
^
In file included from /usr/include/c++/5/memory:79:0,
from /usr/include/asio/detail/addressof.hpp:21,
from /usr/include/asio/detail/handler_alloc_helpers.hpp:19,
from /usr/include/asio/detail/bind_handler.hpp:19,
from /usr/include/asio/detail/wrapped_handler.hpp:18,
from /usr/include/asio/io_service.hpp:24,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/c++/5/functional: In instantiation of ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(std::_Bind<_Functor(_Bound_args ...)>&&) [with _Functor = std::_Mem_fn<long unsigned int (asio::io_service::*)()>; _Bound_args = {asio::io_service}]’:
./main.c:16:130: required from here
/usr/include/c++/5/functional:1120:78: note: synthesized method ‘constexpr std::tuple< <template-parameter-1-1> >::tuple(std::tuple< <template-parameter-1-1> >&&) [with _Elements = {asio::io_service}]’ first required here
: _M_f(std::move(__b._M_f)), _M_bound_args(std::move(__b._M_bound_args))
^
In file included from /usr/include/c++/5/functional:55:0,
from /usr/include/c++/5/memory:79,
from /usr/include/asio/detail/addressof.hpp:21,
from /usr/include/asio/detail/handler_alloc_helpers.hpp:19,
from /usr/include/asio/detail/bind_handler.hpp:19,
from /usr/include/asio/detail/wrapped_handler.hpp:18,
from /usr/include/asio/io_service.hpp:24,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/c++/5/tuple: In instantiation of ‘constexpr std::_Head_base<_Idx, _Head, false>::_Head_base(const _Head&) [with long unsigned int _Idx = 0ul; _Head = asio::io_service]’:
/usr/include/c++/5/tuple:357:21: required from ‘constexpr std::_Tuple_impl<_Idx, _Head>::_Tuple_impl(const _Head&) [with long unsigned int _Idx = 0ul; _Head = asio::io_service]’
/usr/include/c++/5/tuple:473:33: required from ‘constexpr std::tuple< <template-parameter-1-1> >::tuple(const _Elements& ...) [with _Elements = {asio::io_service}]’
/usr/include/c++/5/functional:1114:70: required from ‘std::_Bind<_Functor(_Bound_args ...)>::_Bind(_Functor&&, _Args&& ...) [with _Args = {asio::io_service&}; _Functor = std::_Mem_fn<long unsigned int (asio::io_service::*)()>; _Bound_args = {asio::io_service}]’
/usr/include/c++/5/functional:1468:42: required from ‘typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type std::bind(_Func&&, _BoundArgs&& ...) [with _Func = long unsigned int (asio::io_service::*)(); _BoundArgs = {asio::io_service&}; typename std::_Bind_helper<std::__is_socketlike<_Func>::value, _Func, _BoundArgs ...>::type = std::_Bind<std::_Mem_fn<long unsigned int (asio::io_service::*)()>(asio::io_service)>]’
./main.c:16:130: required from here
/usr/include/c++/5/tuple:108:25: error: use of deleted function ‘asio::io_service::io_service(const asio::io_service&)’
: _M_head_impl(__h) { }
the question: can anyone help me (or point me towards a source of information) understand what's going on here. i suspect the problem is related to the "static" nature of the static_cast...
this possible solution using a lambda function works but i'd be interested to hear opinions on whether it's the "correct" way to do things. personally i also find this easier to parse:
#include <asio.hpp>
#include <thread> // std::thread
#include <functional> // std::bind
int main(int argc, char * argv[]) {
asio::io_service io_service_instance;
auto bound_thing_4 = [&](){
return io_service_instance.run();
};
std::thread mythread(bound_thing_4);
return 0;
}
[EDIT] solution:
it appears instances of asio::io_service do not like to be copied:
#include <asio.hpp>
int main(int argc, char * argv[]) {
asio::io_service io_service_instance;
auto io_service_instance_2 = io_service_instance;
return 0;
}
gives the compiler error:
duncan@casper:/tmp/bind_test$ /usr/bin/g++ -Wall -std=c++11 ./main.c -o test.bin -lpthread
./main.c: In function ‘int main(int, char**)’:
./main.c:5:32: error: use of deleted function ‘asio::io_service::io_service(const asio::io_service&)’
auto io_service_instance_2 = io_service_instance;
^
In file included from /usr/include/asio/basic_io_object.hpp:19:0,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/io_service.hpp:184:7: note: ‘asio::io_service::io_service(const asio::io_service&)’ is implicitly deleted because the default definition would be ill-formed:
class io_service
^
In file included from /usr/include/asio/io_service.hpp:23:0,
from /usr/include/asio/basic_io_object.hpp:19,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/detail/noncopyable.hpp:31:3: error: ‘asio::detail::noncopyable::noncopyable(const asio::detail::noncopyable&)’ is private
noncopyable(const noncopyable&);
^
In file included from /usr/include/asio/basic_io_object.hpp:19:0,
from /usr/include/asio/basic_socket.hpp:20,
from /usr/include/asio/basic_datagram_socket.hpp:20,
from /usr/include/asio.hpp:19,
from ./main.c:1:
/usr/include/asio/io_service.hpp:184:7: error: within this context
class io_service
so the working solution involves passing by reference instead of copying (as per ecatmur's answer):
#include <asio.hpp>
#include <thread> // std::thread
#include <functional> // std::bind
int main(int argc, char * argv[]) {
asio::io_service io_service_instance;
auto bound_thing_3 = std::bind(
static_cast<std::size_t(asio::io_service::*)(void)>(&asio::io_service::run),
std::ref(io_service_instance));
std::thread mythread(bound_thing_3);
return 0;
}
