Re: [Boost-users] filter_iterator and bind

From: David Abrahams (dave_at_[hidden])
Date: 2006-02-21 12:51:48

Nico Galoppo <nico_at_[hidden]> writes:

> I'm having trouble getting make_filter_iterator and bind to work together nicely:
>
> -------------------------------------------------------------------------------
>    boost::function<bool (const node_type&)> is_constraint;
>    is_constraint = boost::bind(&node_type::IsConstraint, _1);
>
>    boost::make_filter_iterator(is_constraint, ab.begin(), ab.end()); // ERROR:
> does not compile
>    boost::make_filter_iterator(boost::bind(&node_type::IsConstraint, _1),
> ab.begin(), ab.end()); // compiles
> -------------------------------------------------------------------------------
>
> Note that ab.begin()/ab.end() return iterators to containers of shared pointers.
> See below for compiler errors.

It's actually not bind, but function.  Bind contains magic that treats
shared_ptr<T> and T& the same way, but for function to take advantage
of that magic, you need to make sure its argument type is
shared_ptr<T>, not T&:

   boost::function<bool (shared_ptr<node_type const>)> is_constraint
      = boost::bind(&node_type::IsConstraint, _1);

   boost::make_filter_iterator(is_constraint, ab.begin(), ab.end());

The hint is right here:

>          Reason: cannot convert from
> 'Hybrid::Graph<node_traits>::const_node_ptr' to 'const node_type'
>          with
>          [
>              node_traits=ArticulatedModelNodeTraits<MyTypes>
>          ]

HTH,

-- 
Dave Abrahams
Boost Consulting
www.boost-consulting.com