Re: [boost] Re: Re: Re: [review] hash functions

From: Peter Dimov (pdimov_at_[hidden])
Date: 2005-03-10 17:51:19

JOAQUIN LOPEZ MU?Z wrote:
>
> The idea is that you can alter only some part of the
> hashing scheme and benefit of the preexisting definitions: [...]

I think I see your point. You want something like this:

template<class F> size_t hash_value( int x, F const & )
{
    return x;
}

template<class F, class T> size_t hash_value( vector<T> const & v, F const & 
f )
{
    return for_each( v.begin(), v.end(), f ).value();
}

which, when combined with a suitable combiner 'f':

class F
{
private:

    // state

public:

    template<class T> void operator()( T const & t )
    {
        // combine state with hash_value( t, F() );
    }

    size_t value() const
    {
        // collapse state into a size_t and return it
    }
};

will automatically propagate it downwards if one invokes hash_value on 
vector<vector<vector<int> > >. Interesting, but overkill, IMO. ;-)