Re: [boost] Movable but not copyable bug?

Subject: Re: [boost] Movable but not copyable bug?
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2014-08-25 17:49:19

Le 25/08/14 23:23, Peter Dimov a écrit :
> Ion Gaztañaga wrote:
>
>> Maybe you should design your code in C++11 and port it to Boost.Move, 
>> you might get better compiler help.
>
> His code compiles in C++11, as is.
I guess that in C++11 Bar<Foo>() is an rvalue that better matches 
Bar(Bar&&) than Bar(const &Bar), but with C++98 Bar<Foo>() is an rvalue 
that matches better const &Bar than Bar(rv<Bar>) as the last need a 
conversion.
>
>> If this copy constructor is instantiated, and in many compilers
>>
>>    Bar<Foo> b(( Bar<Foo>() ));
>>
>> requires the copy constructor, then you get a compilation error. Just 
>> try this equivalent (but more inefficient) code:
>>
>>    Bar<Foo> a;
>>    Bar<Foo> b(a);
>
> This is not equivalent. a is an lvalue here. In the above code, 
> Bar<Foo>() is an rvalue. It should use the move constructor, not the 
> copy constructor.
>
Hi,

I suspect that Bar copy constructor should be available only if T is 
copy constructible. Unfortunately I don't know a way to achieve this.

Best,
Vicente