Re: [Boost-Users] How to use boost::bind

From: Peter Dimov (pdimov_at_[hidden])
Date: 2003-08-26 08:27:12

Darren Cook wrote:
>
> Thanks for the reply. I can almost match that up to the parts in the
> while loop, except mention of "list" is missing. Should it be:
>
>   boost::bind(&Points::add, &list,
>   boost::bind(&Info::key,
>   boost::bind(&InfoContainer::get, &cs, _1))));
>
>> However, if Points is std::set<int>, then "add" should be "insert"
>
> Sorry. Points is a class that can be thought of as a wrapper for std::set.
I
> thought I could simplify the example by substituting, but of course I
hadn't
> thought it through properly had I.
>
> BTW, I was hoping I'd be able to do something like this:
>      std::for_each(c->points.begin(),c->points.end(),
>          list.add(cs.get( _1 )->key)
>           );
>
> But after some experiments with boost::lambda I see why this isn't
> possible. I think if just one call to bind is possible then it is worth
it, but when
> bind is required 2 or more times, falling back to a while loop or a
functor
> seems better. Is anyone else using a similar guideline?

Yes, this is a reasonable guideline, but you should also consider:

1. Adding InfoContainer::get_key as an alias for get(_1)->key

2. Using std::transform with a std::inserter, as Doug already mentioned. An
overcomplicated bind expression sometimes indicates that you're using the
wrong algorithm.

Since Points is not an STL container, std::inserter won't work but one
reasonable alternative would be

template<class It, class F, class L> void transform_and_add(It first, It
last, F f, L & list)
{
    for(; first != last; ++first) list.add( f(*first) );
}

transform_and_add(c->points.begin(), c->points.end(),
    bind(&InfoContainer::get_key, _1), list);