Re: [Boost-users] [Thread] Can't compile package_task code with 1.54

Subject: Re: [Boost-users] [Thread] Can't compile package_task code with 1.54
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2013-06-01 08:38:06

Le 01/06/13 13:53, Vicente J. Botet Escriba a écrit :
> Le 01/06/13 12:34, Szymon Gatner a écrit :
>> Hi Vincente,
>>
>>     I have found the error. My tests don't test for
>>     packaged_task<void()>.
>>
>>     The following patch should fix the issue (see attached file)
>>
>>     Please could you apply it a tell me if it fix with your compiler?
>>
>>
>> I am happy to confirm the fix, really appreciate so quick response 
>> from you. To clarify: I was using boost_1_54_0_beta1_rc1.7z from beta 
>> announcement.
>>
>>
>> Btw: I am using a workaround for packaged_task to be able store it in 
>> std/boost::function:
>>
>>       typedef boost::packaged_task<Ret()> Task;
>>       typedef boost::shared_ptr<Task> TaskPtr;
>>       TaskP task(new Task(f));
>>       addTask(boost::bind(&Task::operator (), task));
>>
>> where:
>>
>>       void addTask(boost::function<void()> task);
>>
>>
>> not a problem of course but with 1.54 beta I was still not able to 
>> just move packaged_task to function directly:
>>
>>   boost::packaged_task<void()> t1;
>>
>>   boost::function<void()> f2(boost::move(t1));
>>
>> gives:
>>
>> Error1error C2248: 
>> 'boost::packaged_task<<unnamed-symbol>>::packaged_task' : cannot 
>> access private member declared in class 
>> 'boost::packaged_task<<unnamed-symbol>>'d:\devel\boost_1_54_0_beta1\boost\function\function_template.hpp1070ConsoleApplication2
>>
>> same error with std::function.
>>
>> Is this an issue with packaged_task or a std/boost function 
>> implementations. I think boost::functions are not movable so they 
>> probably try to copy packaged_task but not sure why it also doesn't 
>> work with std::function.
>>
>>
> IMO boost::function doesn't supports move semantics. I will take a 
> look at std::function. Could you post the error with std::function?
>
I don't find a constructor of function from a rvalue functor.

 From the standard:
template<class F> function(F f);
template <class F, class A> function(allocator_arg_t, const A& a, F f);
7 Requires: F shall be *CopyConstructible*. f shall be Callable 
(20.10.11.2) for argument types ArgTypes
and return type R. The copy constructor and destructor of A shall not 
throw exceptions.
8 Postconditions: !*this if any of the following hold:
--- f is a NULL function pointer.
--- f is a NULL pointer to member.
--- F is an instance of the function class template, and !f
9 Otherwise, *this targets a copy of f initialized with std::move(f). 
[Note: Implementations are
encouraged to avoid the use of dynamically allocated memory for small 
callable objects, for example,
where f's target is an object holding only a pointer or reference to an 
object and a member function
pointer. --- end note ]
10 Throws: shall not throw exceptions when f is a function pointer or a 
reference_wrapper<T> for some
T. Otherwise, may throw bad_alloc or any exception thrown by F's copy or 
move constructor.

But I find an assignment

template<class F> function& operator=(F&& f);
18 Effects: function(std::forward<F>(f)).swap(*this);
19 Returns: *this

This seems confusing. What am I missing?

Best,
Vicente