Boost logo

Boost :

From: jkharris01 (john.harris_at_[hidden])
Date: 2002-02-20 18:15:57

Should bind() be extended to include binding to member data? If it
already allows convenient binding to member functions, wouldn't
member data be a natural extension?

Perhaps the operator() of the class resulting from such a bind would
return a reference to the member data.

I've run this by the author of boost::function, Douglas Gregor
(privately), and he thinks it would be a useful addition.

The specific problem that got me thinking about this is that I
couldn't find an easy way to make a predicate compare only
the ".second" member of a pair, as in a map lookup by value:

    typedef std::map<int,float> map_t;

    // find the map entry whose value is 3.14
    void findpi(const map_t& themap)
        std::find_if(themap.begin(), themap.end(),
                     member_equal(&map_t::value_type::second, 3.14));

My solution to this, by the way, goes like this:

template<typename R, typename T>
class MemData_t
        MemData_t(R T::* pmd_)
                : pmd(pmd_)
        const R& operator()(const T& inst_)
                return inst_.*pmd;
        R T::* pmd; // ptr to member data

template <typename T, typename R> boost::function<bool,T>
member_equal(R T::* pmd_, R stator_)
        return boost::bind<bool>(
            boost::bind<const R&>(MemData_t<R,T>(pmd_),_1),

Boost list run by bdawes at, gregod at, cpdaniel at, john at