我正在尝试将一些使用不同系统的代码转换为使用 Boost.Signals2。旧代码使用常规函数指针作为函子;连接是通过使用函子调用特定方法来完成的,而断开连接是通过使用完全相同的函子调用另一个方法来完成的。出于兼容性原因,我仍然希望支持这一点,即使我知道这不是 Signals2 下最有效的方法。
namespace bs2 = boost::signals2;
class Foo
{
typedef bs2::signal<void (const Foo *foo)> UpdateEvent;
UpdateEvent m_UpdateEvent;
public:
typedef UpdateEvent::slot_type UpdateCallback;
bs2::connection Register(const UpdateCallback& callback)
{
return m_UpdateEvent.connect(callback);
}
void Unregister(const UpdateCallback& callback)
{
m_UpdateEvent.disconnect(callback);
}
};
上面的(简化的)代码可以很好地连接,但是 Unregister 方法在 VS2008 中不能编译:
T:\boost\boost_1_47_0\boost/function_equal.hpp(17) : error C2678: binary '==' : no operator found which takes a left-hand operand of type 'const Foo::UpdateCallback' (or there is no acceptable conversion)
T:\boost\boost_1_47_0\boost/function/function_base.hpp(808): could be 'bool boost::operator ==<T>(const boost::function_base &,Functor)'
with
[
T=Foo::UpdateCallback,
Functor=Foo::UpdateCallback
]
T:\boost\boost_1_47_0\boost/function/function_base.hpp(817): or 'bool boost::operator ==<F>(Functor,const boost::function_base &)'
with
[
F=Foo::UpdateCallback,
Functor=Foo::UpdateCallback
]
C:\Program Files\Microsoft SDKs\Windows\v6.0A\include\guiddef.h(192): or 'int operator ==(const GUID &,const GUID &)' [found using argument-dependent lookup]
T:\boost\boost_1_47_0\boost/function/function_base.hpp(746): or 'bool boost::operator ==(const boost::function_base &,boost::detail::function::useless_clear_type *)'
T:\boost\boost_1_47_0\boost/function/function_base.hpp(758): or 'bool boost::operator ==(boost::detail::function::useless_clear_type *,const boost::function_base &)'
T:\boost\boost_1_47_0\boost/blank.hpp(58): or 'bool boost::operator ==(const boost::blank &,const boost::blank &)'
while trying to match the argument list '(const Foo::UpdateCallback, const Foo::UpdateCallback)'
T:\boost\boost_1_47_0\boost/function_equal.hpp(24) : see reference to function template instantiation 'bool boost::function_equal_impl<F,G>(const F &,const G &,long)' being compiled
with
[
F=Foo::UpdateCallback,
G=Foo::UpdateCallback
]
T:\boost\boost_1_47_0\boost/function/function_base.hpp(811) : see reference to function template instantiation 'bool boost::function_equal<Functor,Functor>(const F &,const G &)' being compiled
with
[
Functor=Foo::UpdateCallback,
F=Foo::UpdateCallback,
G=Foo::UpdateCallback
]
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(527) : see reference to function template instantiation 'bool boost::operator ==<T>(const boost::function_base &,Functor)' being compiled
with
[
T=Foo::UpdateCallback,
Functor=Foo::UpdateCallback
]
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(221) : see reference to function template instantiation 'void boost::signals2::detail::signal1_impl<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::do_disconnect<T>(const T &,boost::mpl::bool_<C_>)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback,
C_=false
]
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(691) : see reference to function template instantiation 'void boost::signals2::detail::signal1_impl<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::disconnect<T>(const T &)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback
]
.\Foo.cpp(72) : see reference to function template instantiation 'void boost::signals2::signal1<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::disconnect<Foo::UpdateCallback>(const T &)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback
]
那么,不知何故,函数对象不能与自身进行比较?我还尝试将 slot_function_type 用于 UpdateCallback,并明确将其指定为具有相同签名的 boost::function;这两个都产生了这个错误:
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(527) : error C2666: 'boost::signals2::detail::operator ==' : 4 overloads have similar conversions
T:\boost\boost_1_47_0\boost/function/function_template.hpp(997): could be 'void boost::operator ==<R,T0>(const boost::function1<R,T0> &,const boost::function1<R,T0> &)' [found using argument-dependent lookup]
with
[
R=void,
T0=const Foo *
]
T:\boost\boost_1_47_0\boost/function/function_base.hpp(817): or 'bool boost::operator ==<boost::function<Signature>>(Functor,const boost::function_base &)' [found using argument-dependent lookup]
with
[
Signature=void (const Foo *),
Functor=boost::function<void (const Foo *)>
]
T:\boost\boost_1_47_0\boost/function/function_base.hpp(808): or 'bool boost::operator ==<T>(const boost::function_base &,Functor)' [found using argument-dependent lookup]
with
[
T=Foo::UpdateCallback,
Functor=Foo::UpdateCallback
]
or 'built-in C++ operator==(void (__thiscall boost::function1<R,T0>::dummy::* )(void), void (__thiscall boost::function1<R,T0>::dummy::* )(void))'
with
[
R=void,
T0=const Foo *
]
while trying to match the argument list '(boost::function<Signature>, const Foo::UpdateCallback)'
with
[
Signature=void (const Foo *)
]
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(221) : see reference to function template instantiation 'void boost::signals2::detail::signal1_impl<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::do_disconnect<T>(const T &,boost::mpl::bool_<C_>)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback,
C_=false
]
T:\boost\boost_1_47_0\boost/signals2/detail/signal_template.hpp(691) : see reference to function template instantiation 'void boost::signals2::detail::signal1_impl<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::disconnect<T>(const T &)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback
]
.\Foo.cpp(72) : see reference to function template instantiation 'void boost::signals2::signal1<R,T1,Combiner,Group,GroupCompare,SlotFunction,ExtendedSlotFunction,Mutex>::disconnect<Foo::UpdateCallback>(const T &)' being compiled
with
[
R=void,
T1=const Foo *,
Combiner=boost::signals2::optional_last_value<void>,
Group=int,
GroupCompare=std::less<int>,
SlotFunction=boost::function<void (const Foo *)>,
ExtendedSlotFunction=boost::function<void (const boost::signals2::connection &,const Foo *)>,
Mutex=boost::signals2::mutex,
T=Foo::UpdateCallback
]
所以我想它已经从选择太少变成了太多。我该如何解决这个问题?