Re: [boost] Movable but not copyable bug?

Subject: Re: [boost] Movable but not copyable bug?
From: Mostafa (mostafa_working_away_at_[hidden])
Date: 2014-08-25 19:36:56

On Mon, 25 Aug 2014 16:18:28 -0700, Peter Dimov <lists_at_[hidden]> wrote:

> Mostafa wrote:
>> Then why is it that in C++03 with g++ 4.8.2 the code sample compiles if  
>> the copy ctor for Bar is not explicitly defined?
>
> C++03 12.8/5:
>
> The implicitly-declared copy constructor for a class X will have the form
> X::X(const X&)
> if
> — each direct or virtual base class B of X has a copy constructor whose  
> first parameter is of type const
> B& or const volatile B&, and
> — for all the nonstatic data members of X that are of a class type M (or  
> array thereof), each such class type
> has a copy constructor whose first parameter is of type const M& or  
> const volatile M&.107)
> Otherwise, the implicitly declared copy constructor will have the form
> X::X(X&)
>
> My guess is that Boost.Move declares Foo's copy constructor to take  
> Foo&. This causes Bar's implicit copy constructor to take Bar&, which  
> doesn't match rvalues.

(Filling in the details.)
Ah, so in that case Bar's move ctor is selected:

   Bar(BOOST_RV_REF(Bar) rhs)
   : f(::boost::move(rhs.f))
   {}

because "Bar<Foo>()" is implicitly convertible to BOOST_RV_REF(Bar).

Thanks,

Mostafa