transform

#include <algorithm>
#include <iostream>
#include <vector>
                                                                                                                
using std::vector,
    std::transform,
    std::cerr;

#define TRANSFORM_1

class Temp{
    public:
        int a, b;
        Temp(int i, int j):a(i), b(j){}
};

bool operator==(const Temp& l, const Temp& r)
{
    return l.a == r.a && l.b == r.b;
} 
                        
typedef vector<Temp> my_vector;
            
int main(){
    my_vector a = {Temp(0, 0), Temp(1, 1), Temp(2, 4), Temp(3, 9)};
    my_vector b = {Temp(2, 4), Temp(17, 289), Temp(18, 324), Temp(19, 361)};

    auto print = [] (Temp t){
        cerr << "Temp(" << t.a << ", " << t.b << ")\n";
    };  

    cerr << "a before transform:\n";
    for_each(a.begin(), a.end(), print);
    cerr << "b before transform:\n";
    for_each(b.begin(), b.end(), print);
    cerr << "\n";

#ifdef TRANSFORM_1    
   
    auto test = [] (Temp t)->Temp{
        t.a *= 4;
        t.b += 2;
        return t;
    };

    transform(a.begin(), a.end(), b.begin(), test);

    cerr << "a after TRANSFORM_1:\n";
    for_each(a.begin(), a.end(), print);
    cerr << "b after TRANSFORM_1:\n";
    for_each(b.begin(), b.end(), print);
    cerr << "\n";

#else
    auto binary_test = [] (Temp &t, Temp &u)->Temp{
        t.a *= 4;
        t.b += 2;
        u.a *=2;
        u.b += 5;
        return t;
    };

    my_vector c = {Temp(2, 4), Temp(17, 289), Temp(18, 324), Temp(19, 361)};
    transform(a.begin(), a.end(), b.begin(), c.begin(), binary_test);
    cerr << "a after transform 2:\n";
    for_each(a.begin(), a.end(), print);
    cerr << "b after transform 2:\n";
    for_each(b.begin(), b.end(), print);
    cerr << "c after transform 2:\n";
    for_each(c.begin(), c.end(), print);
#endif
    return 0;
}