Boost logo

Boost :

Subject: Re: [boost] Movable but not copyable bug?
From: Mostafa (mostafa_working_away_at_[hidden])
Date: 2014-08-25 19:05:11

On Mon, 25 Aug 2014 15:23:23 -0700, Ion Gaztañaga <igaztanaga_at_[hidden]>

> El 25/08/2014 23:23, Peter Dimov escribió:
>> 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.
>>> 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.
> Yes, but he is compiling in C++03, that's why he's getting:
> error: passing ‘const Foo’ as ‘this’ argument of ‘Foo::operator
> boost::rv<Foo>&()’ discards qualifiers [-fpermissive]
> In C++03 both will require the copy constructor (I think).

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? My understanding is that
in that case the copy ctor is *not* deleted, because the following

   // (3)
   Bar<int> b2(( Bar<int>() ));

(Note, the definition of Foo's ctor has been changed to just take one arg
and Bar's ctor has been updated accordingly.)

Boost list run by bdawes at, gregod at, cpdaniel at, john at