(C++) ExtractIds

 

ExtractIds is a container code snippet to extract a certain data type from multiple complex class instances.

 

ExtractIds extracts the integer called ID from multiple Person class instances stored in a std::vector. Note that the container the Persons are stored in will support the example code below.

 

---

#include <algorithm> #include <cassert> #include <vector> #include <boost/lambda/bind.hpp> #include <boost/lambda/lambda.hpp> #include <boost/shared_ptr.hpp> struct Person {   Person(const int id) : m_id(id) {}   int GetId() const { return m_id; }   private:   int m_id; }; const std::vector<int> ExtractIds1(const std::vector<Person>& v) {   std::vector<int> w;   std::transform(     v.begin(),     v.end(),     std::back_inserter(w),     boost::lambda::bind(&Person::GetId, boost::lambda::_1)     );   return w; } const std::vector<int> ExtractIds2(const std::vector<Person*>& v) {   std::vector<int> w;   std::transform(     v.begin(),     v.end(),     std::back_inserter(w),     boost::lambda::bind(&Person::GetId, boost::lambda::_1)     );   return w; } const std::vector<int> ExtractIds3(const std::vector<boost::shared_ptr<Person> >& v) {   std::vector<int> w;   std::transform(     v.begin(),     v.end(),     std::back_inserter(w),     boost::lambda::bind(&Person::GetId, *boost::lambda::_1) //Note the asterisk     );   return w; } int main() {   {     std::vector<Person> v;     v.push_back(Person(1));     v.push_back(Person(4));     v.push_back(Person(9));     v.push_back(Person(6));     const std::vector<int> w = ExtractIds1(v);     assert(w.size() == 4);     assert(w[0] == 1);     assert(w[1] == 4);     assert(w[2] == 9);     assert(w[3] == 6);   }   {     std::vector<Person*> v;     v.push_back(new Person(1));     v.push_back(new Person(4));     v.push_back(new Person(9));     v.push_back(new Person(6));     const std::vector<int> w = ExtractIds2(v);     assert(w.size() == 4);     assert(w[0] == 1);     assert(w[1] == 4);     assert(w[2] == 9);     assert(w[3] == 6);     delete v[0];     delete v[1];     delete v[2];     delete v[3];   }   {     std::vector<boost::shared_ptr<Person> > v;     v.push_back(boost::shared_ptr<Person>(new Person(1)));     v.push_back(boost::shared_ptr<Person>(new Person(4)));     v.push_back(boost::shared_ptr<Person>(new Person(9)));     v.push_back(boost::shared_ptr<Person>(new Person(6)));     const std::vector<int> w = ExtractIds3(v);     assert(w.size() == 4);     assert(w[0] == 1);     assert(w[1] == 4);     assert(w[2] == 9);     assert(w[3] == 6);   } }