Must I use boost::bind to create polymorphic "transform" functionality?

Question

I am trying to call a member function on each object in a vector, with a specified parameter, and I would like the call to be polymorphic. I believe the function vstuff shown below achieves this. But can vstuff be modified to take a vector< shared_ptr < Base> > without using boost::bind?

class Base{
            virtual double stuff(double t);
           }
//and some derived classes overriding stuff
//then in some code 
vector<double> vstuff(double t, vector<Base*> things)
{
vector<double> vals;
vals.resize(things.size());
transform(things.begin(), things.end(), vals.begin(), std::bind2nd(std::mem_fun(&Base::stuff),t));
return vals;
}

I know that shared_ptr s require mem_fn instead of mem_fun , but I have not succeeded in making mem_fn work with the bind2nd I need to pass in the parameter t, so I wonder whether or not it is feasible.. ?

Answer 1

You can use std::bind too (or lambdas):

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#include <algorithm>
#include <vector>
#include <memory>

struct Base {
    virtual double stuff(double) { return 0; }
};

struct Threes : Base {
    virtual double stuff(double) { return 3; }
};

struct Sevens : Base {
    virtual double stuff(double) { return 7; }
};

std::vector<double> vstuff(double t, std::vector<std::shared_ptr<Base> > things)
{
    std::vector<double> vals;
    vals.resize(things.size());
    transform(things.begin(), things.end(), vals.begin(), std::bind(&Base::stuff, std::placeholders::_1, t));
    return vals;
}

#include <iostream>

int main() {
    for (double v : vstuff(42, {
                std::make_shared<Sevens>(),
                std::make_shared<Sevens>(),
                std::make_shared<Sevens>(),
                std::make_shared<Threes>(),
                std::make_shared<Sevens>(),
                std::make_shared<Threes>(),
                std::make_shared<Sevens>(),
                std::make_shared<Sevens>(),
                std::make_shared<Threes>(),
                std::make_shared<Sevens>(),
            }))
    {
        std::cout << v << " ";
    }
}

Prints

7 7 7 3 7 3 7 7 3 7