From: Andrej van der Zee (mavdzee_at_[hidden])
Date: 2007-06-13 03:10:23
Hi,
Indeed everything compiles again with boost 1.34!
Thanks alot,
Andrej
--- Joaquín Mª López Muñoz <joaquin_at_[hidden]> wrote:
> Hello Andrej,
>
> Andrej van der Zee ha escrito:
>
> > Hi,
> >
> > I'm trying to store these classes in a
> multi_index:
> >
> > struct Foo
> > {
> > int a;
> > };
> >
> > struct Bar
> > :Foo
> > {
> > };
> >
> > typedef multi_index_container<
> > Bar,
> > indexed_by<
> > ordered_unique<
> > member<Foo, int, &Bar::a>
> > >
> > >
> > > Bar_container;
> >
> > Notice I have to use "Foo" in the "member<" line.
>
> Yes, this is an odd C++ restriction with pointers to
> member functions
> when used as non-type template parameters: although
> Bar inherits
> from Foo, &Bar::a (which is an alias for &Foo::a) is
> not seen (statically)
> as a valid int (Bar:: *) --usual base-derived
> relationships don't apply
> here. That's why you had to use Foo as the base
> class of member.
> BTW, the expression
>
> member<Foo, int, &Bar::a>
>
> is entirely equivalent to
>
> member<Foo, int, &Foo::a>
>
> although the latter is probably clearer.
>
> > However, even with this, when trying to do a
> search:
> > [...]
> > I get this:
> >
> > /usr/include/boost/multi_index/member.hpp:
> > [...]
> > multitest2.cc:55: instantiated from here
> > /usr/include/boost/multi_index/member.hpp:84:
> error:
> > no match for
> > 'operator*' in '*x'
> >
> > I've tried a few alternatives such as providing a
> custom compare function
> > but I always get this error. It seems to have
> something to do with the
> > fact that the key is in the base class. If I move
> the key to the derived
> > class (and change the "member<" line), it works
> fine.
> >
> > Surely there's a way to do this. Anyone know how ?
> >
> > Using gcc version 4.1.2 20061115 (prerelease)
> (Debian
> > 4.1.1-21) and
> > libboost 1.33.1.
>
> Your code will work out of the box with Boost 1.34,
> where some issues
> about key extractors being fed derived classes are
> solved (see bullet 3 of
>
http://boost.org/libs/multi_index/doc/release_notes.html#boost_1_34
> ).
> In case you can't upgrade to Boost 1.34, you can use
> a custom key
> extractor to work around the problem:
>
> struct Bar_a_extractor
> {
> typedef int result_type;
>
> int operator()(const Bar& b)const
> {
> return b.a;
> }
> };
>
> using namespace boost::multi_index;
>
> typedef multi_index_container<
> Bar,
> indexed_by<
> ordered_unique<
> Bar_a_extractor
> >
> >
> > Bar_container;
>
> Hope this helps,
>
> Joaquín M López Muñoz
> Telefónica, Investigación y Desarrollo
>
> _______________________________________________
> Boost-users mailing list
> Boost-users_at_[hidden]
>
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>
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