Does this work? struct f : public std::unary_function { int operator()(int& x) { return x; } }; -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Nicola Sent: 11 April 2008 10:11 To: boost-users@lists.boost.org Subject: [Boost-users] [iterator] Writable transform_iterator: how to? Hello, I cannot figure out why the following code is wrong: #include <iostream> #include <vector> #include <functional> #include struct f : public std::unary_function { int& operator()(int& x) { return x; } }; typedef std::vector<int> vec_type; typedef boost::transform_iterator trans_iter_type; int main() { vec_type V; V.push_back(4); trans_iter_type it(boost::make_transform_iterator(V.begin(), f())); std::cout << *it << std::endl; *it = 8; std::cout << *it << std::endl; return 0; } The compiler (g++ 4.0.1) complains about dereferencing and the error message says: error: passing ‘const f’ as ‘this’ argument of ‘int& f::operator()(int&)’ discards qualifiers Nicola ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ ****************************************************************************** "This message and any attachments are solely for the intended recipient and may contain confidential and privileged information. If you are not the intended recipient, any disclosure, copying, use, or distribution of the information included in this message and any attachments is prohibited. If you have received this communication in error, please notify us by reply e-mail and immediately and permanently delete this message and any attachments. Thank you." Interactive Transaction Solutions Ltd (2473364 England) Registered Office: Systems House, Station Approach Emsworth PO10 7PW ********************************************************************** Ce message �lectronique contient des informations confidentielles � l'usage unique des destinataires indiqu�s, personnes physiques ou morales. Si vous n'�tes pas le destinataire voulu, toute divulgation, copie, ou diffusion ou toute autre utilisation de ces informations, est interdite. Si vous avez re�u ce message �lectronique par erreur, nous vous remercions d'en avertir son exp�diteur imm�diatement par email et de d�truire ce message ainsi que les �l�ments attach�s. Interactive transaction Solutions SAS- France (RCS Pontoise : 489 397 877) Si�ge social : Parc Saint Christophe, 10, Avenue de l�Entreprise 95865 Cergy-Pontoise Cedex ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________

I've had to comment out the line //*it = 8; but the rest works under VC8 and increments the value in the vector: struct f : public std::unary_function { int operator()(int x) const { return ++x; } }; typedef std::vector<int> vec_type; typedef boost::transform_iterator trans_iter_type; int _tmain(int argc, _TCHAR* argv[]) { vec_type V; V.push_back(4); trans_iter_type it(boost::make_transform_iterator(V.begin(),f())); std::cout << *it << std::endl; //*it = 8; std::cout << *it << std::endl; return 0; } -----Original Message----- From: boost-users-bounces@lists.boost.org [mailto:boost-users-bounces@lists.boost.org] On Behalf Of Nicola Sent: 11 April 2008 10:11 To: boost-users@lists.boost.org Subject: [Boost-users] [iterator] Writable transform_iterator: how to? Hello, I cannot figure out why the following code is wrong: #include <iostream> #include <vector> #include <functional> #include struct f : public std::unary_function { int& operator()(int& x) { return x; } }; typedef std::vector<int> vec_type; typedef boost::transform_iterator trans_iter_type; int main() { vec_type V; V.push_back(4); trans_iter_type it(boost::make_transform_iterator(V.begin(), f())); std::cout << *it << std::endl; *it = 8; std::cout << *it << std::endl; return 0; } The compiler (g++ 4.0.1) complains about dereferencing and the error message says: error: passing ‘const f’ as ‘this’ argument of ‘int& f::operator()(int&)’ discards qualifiers Nicola ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________ ****************************************************************************** "This message and any attachments are solely for the intended recipient and may contain confidential and privileged information. If you are not the intended recipient, any disclosure, copying, use, or distribution of the information included in this message and any attachments is prohibited. If you have received this communication in error, please notify us by reply e-mail and immediately and permanently delete this message and any attachments. Thank you." Interactive Transaction Solutions Ltd (2473364 England) Registered Office: Systems House, Station Approach Emsworth PO10 7PW ********************************************************************** Ce message �lectronique contient des informations confidentielles � l'usage unique des destinataires indiqu�s, personnes physiques ou morales. Si vous n'�tes pas le destinataire voulu, toute divulgation, copie, ou diffusion ou toute autre utilisation de ces informations, est interdite. Si vous avez re�u ce message �lectronique par erreur, nous vous remercions d'en avertir son exp�diteur imm�diatement par email et de d�truire ce message ainsi que les �l�ments attach�s. Interactive transaction Solutions SAS- France (RCS Pontoise : 489 397 877) Si�ge social : Parc Saint Christophe, 10, Avenue de l�Entreprise 95865 Cergy-Pontoise Cedex ______________________________________________________________________ This email has been scanned by the MessageLabs Email Security System. For more information please visit http://www.messagelabs.com/email ______________________________________________________________________