Re: [Boost-users] [Statechart] Passing referencetocreate_processor()

Subject: Re: [Boost-users] [Statechart] Passing referencetocreate_processor()
From: Andreas Huber (ahd6974-spamboostorgtrap_at_[hidden])
Date: 2009-04-23 18:24:14

Hi Peter

Thanks for looking at this!

>> I must admit I don't currently see why this happens, I'll probably have 
>> to produce a minimal repro and ask bind experts for help.
>
> It happens because ultimately you produce a bind expression such as
>
>    boost::bind( pImpl, this, ..., boost::ref( value ) )
>
> and the ref is interpreted by bind as a reference to 'value'. But your 
> Arg1 remains a reference_wrapper. You'll probably need to convert ArgN 
> parameters that are of the form reference_wrapper<X> to X& before 
> instantiating create_processor_implN.

Ok, lets see whether I understand this correctly:

#include <boost/noncopyable.hpp>
#include <boost/bind.hpp>

class Object : public boost::noncopyable {};

void func1(Object &) {}
void func2(boost::reference_wrapper<Object>) {}

int main()
{
    Object value;
    boost::bind(&func1, boost::ref(value))(); // 1: compiles
    boost::bind(&func2, boost::ref(value))(); // 2: doesn't
    return 0;
}

2 doesn't compile because bind internally assumes that the target function 
accepts a T & parameter for each reference_wrapper<T> argument, correct?

If so, then I guess I should use boost::unwrap_reference<Arg1>::type instead 
of Arg1 to instantiate create_processor_impl1.

Thanks & Regards,

-- 
Andreas Huber
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