Re: [boost] [multi_index] Problems with chained pointers in multi index from 1.34 RC

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2006-04-12 12:58:54

Hello Alexei, thank you for testing the RC branch before
it's out, this certainly helps ship a more robust library!

----- Mensaje original -----
De: Alexei Alexandrov <alexei.alexandrov_at_[hidden]>
Fecha: Miércoles, Abril 12, 2006 6:15 pm
Asunto: [boost] [multi_index] Problems with chained pointers in multi 
index from 1.34 RC

> Hi,
> 
> my multi_index use case:
>  * The container contains not objects themselves, but pointers 
> (shared_ptr-s).
>  * The objects are noncopyable - they are created by a factory 
> and only smart 
> pointers are copied between clients.
>  * The container has 2 indexes. Indexes are built on const_mem_fn 
> extractor. 
> One of the indexes uses a function from a base class.
> 
> It seems that in 1.34 problem with using member function from a 
> base class is 
> supposed to be solved, but it causes a regression that you cannot 
> have pointers 
> to noncopyable objects in the container. Is this a known issue?

No, it is not. Alas I'm rather computer-disabled until next week,
so I can't directly try to reproduce the problem, in the meantime
I'd be very greateful if you can provide more info on the
following:

1. What is the compiler error you're getting?
2. The difference between 1.33.1 and 1.34 is that one of the
overloads inside const_mem_fun is now restricted by means of
boost::disable_if:

  typename disable_if<
    is_convertible<const ChainedPtr,const Class>,Type>::type
  operator()(const ChainedPtr& x)const
  {
    return operator()(*x);
  }

Now, from what you report, seems the restriction is
being too much comprehensive. Could you test what is the
value of

  boost::is_convertible<
    const name_record::Ptr,
    const name_record
  >::value

on your compiler? If this evaluates to true (or fails to
compile), then we've got both an explanation for the problem
and a serious issue with boost::is_convertible. I've googled
for "is_convertible noncopyable" and found some references
about problems with using is_convertible on non-copyable
types, but the references are too vague and distant in the
past to consider worth referring to.

Again, thank you for using Boost.MultiIndex and being
such an early tester of the RC branch. Looking fwd to getting
your feedback wrt to the questions above.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo