[Boost-users] bind depending on the type

From: Minkoo Seo (minkoo.seo_at_[hidden])
Date: 2006-08-19 13:54:34

Hi list.

I'm trying to find out the way to bind depending on the types
in a lambda expression.

Let's take the following as an example:

#include <iostream>
#include <vector>
#include <numeric>
#include <boost/lambda/lambda.hpp>
#include <boost/lambda/bind.hpp>

using namespace std;
using namespace boost::lambda;

int main()
{
    vector< pair<string, int> > subjects;
    subjects.push_back(make_pair("Math", 90));
    subjects.push_back(make_pair("English", 86));
    subjects.push_back(make_pair("Physics", 88));
    subjects.push_back(make_pair("Biology", 97));

    long total;
    total = accumulate(subjects.begin(), subjects.end(), 0,
                _1 + bind(&pair<string, int>::second, _2));

    cout << "total score: " << total << endl;

    return EXIT_SUCCESS;
}

This is a simple score card application that computes the total score.
As you can see, I've used bind in calling accumulate and that
seems to be ugly. So, I modified the code as follows:

#define get_score(p) (bind(&pair<string, int>::second, p))
..
total = accumulate(subjects.begin(), subjects.end(), 0, _1 + get_score(_2));

This seems to be pretty. But the problem is that this code depends
on the fact that _1 is int while _2 is pair<string, int>. I don't know whether
this is platform independent, and this code still seems to be weird anyway.

So, what I want to do is write a function get_score that successfuly
compiles and run the following:

total = accumulate(subjects.begin(), subjects.end(), 0, get_score(_1) +
get_score(_2));

I've tried my best only to fail. Could anybody write get_score functions for me?

Thanks in advance.

Sincerely,
Minkoo Seo