使用boost copy将struct的成员作为键映射复制到set容器中

Question

Having struct below:

struct MixingParts{
int intPart;
double doublePart;
}

and std::map as follow:

std::map<MixingParts, std::vector<int> > MixingMap;

I found boost::copy very useful, I will appreciate if you please help me to only extract integer part of struct as key of the above map and insert it back to the std::set intSet;

boost::copy(MixingMap | boost::adoptors::map_keys(.....*Is it possible to use bind here?*...), std::inserter(intSet, intSet.begin())

I can only use C++98, and also any other solution which is less verbose and optimized is appreciated.

Answer 1

boost::transform(mm, std::mem_fn(&MixingParts::intPart), 
    std::inserter(intSet, intSet.begin())));

Or use copy / copy_range with transformed adaptor

Here's an integrated live example:

Live On Coliru

#include <boost/range/adaptors.hpp>
#include <boost/range/algorithm.hpp>
#include <iostream>

struct MixingParts{
    int intPart;
    double doublePart;
};

using boost::adaptors::transformed;

int main() {

    std::vector<MixingParts> v { { 1,0.1 }, {2, 0.2}, {3,0.3} };

    boost::copy(v | transformed(std::mem_fn(&MixingParts::intPart)),
            std::ostream_iterator<int>(std::cout, " "));
}

Prints

1 2 3 

boost::mem_fn can be used too.

Answer 2

for (MixingMap::const_iterator it = mm.begin(); it != mm.end(); ++it)
    intSet.insert(it->first.intPart);

It would be less verbose in C++11, but it's hardly bloated by C++98 standards. And it's simple and optimally efficient (given the choice of data structures).