Re: [Boost-users] [multi_index] illegal indirection compile error

From: JOAQUIN LOPEZ MU?Z (joaquin_at_[hidden])
Date: 2006-07-31 14:41:47

----- Mensaje original -----
De: Themistoklis Bourdenas <themis_at_[hidden]>
Fecha: Lunes, Julio 31, 2006 4:47 pm
Asunto: [Boost-users] [multi_index] illegal indirection compile error

> Could you help me understand what I'm doing wrong in the code 
> below? I'm 
> trying to setup a multi_index structure of class B.
> 
> class A
> {
> 	const std::string& ID(void) const;
> 	...
> };
> 
> class B : public A
> {
> 	...
> };
> 
> typedef boost::multi_index::multi_index_container<
> 	B*,
> 	boost::multi_index::indexed_by<
>        	boost::multi_index::ordered_unique<
>                	boost::multi_index::const_mem_fun<A, const 
> std::string&, &A::ID>
>        	>
> 	>
> > BSet;
> 
> However when I compile VS2005 returns me an "illegal indirection" 
> compile error. Any thoughts?

Hello Themistoklis,

You've found a limitation in Boost.MultiIndex (as of Boost
1.33.1) by which one cannot specifiy a key in a given base
class and pass derived classes as elements. This is solved
in what will become Boost 1.34, please read bullet 3 of
Boost.MultiIndex release notes at:

http://boost-
consulting.com/boost/libs/multi_index/doc/release_notes.html#boost_1_34

Until this release is out, you can use the following
workarond: simply define a custom key extractor like this
(warning, I haven't compiled it, beware typos):

struct pB_ID_extractor
{
  typedef std::string result_type;
  const std::string& operator()(const B* pb)const
  {
    return pb->ID();
  }
};

typedef boost::multi_index::multi_index_container<
  B*,
  boost::multi_index::indexed_by<
    boost::multi_index::ordered_unique<
      pB_ID_extractor
    >
  >
> BSet;

Does this help? Thank you for using Boost.MultiIndex,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo