[mem_fn] return type
I am having trouble understanding the return type of mem_fn. Is it possible to create a vector of this type, analogous to how one can create a vector of type mem_fun_t to hold the return values of mem_fun()? Here is an example of what I'd like to do. Thanks in advance. #include <vector> #include <functional> #include "boost/shared_ptr.hpp" #include "boost/mem_fn.hpp" class A { public: A(const int a) : a_(a) {} const int get() const {return a_;} private: int a_; }; int main(int argc, char** argv) { // I can do this std::vector<std::const_mem_fun_t<const int, A> > v; v.push_back(std::mem_fun(&A::get)); int i = v[0](new A(4)); // and this boost::shared_ptr<A> p(new A(7)); int j = boost::mem_fn(&A::get)(p); // but how do I do this? // std::vector< WHAT GOES HERE > w; // w.push_back(boost::mem_fn(&A::get)); // int k = w[0](p); return 0; }
On Mon, Aug 31, 2009 at 9:33 PM, Lowell McLinskey<lmclinskey@gmail.com> wrote:
I am having trouble understanding the return type of mem_fn. Is it possible to create a vector of this type, analogous to how one can create a vector of type mem_fun_t to hold the return values of mem_fun()? Here is an example of what I'd like to do. Thanks in advance. #include <vector> #include <functional> #include "boost/shared_ptr.hpp" #include "boost/mem_fn.hpp" class A { public: A(const int a) : a_(a) {} const int get() const {return a_;} private: int a_; }; int main(int argc, char** argv) { // I can do this std::vector<std::const_mem_fun_t<const int, A> > v; v.push_back(std::mem_fun(&A::get)); int i = v[0](new A(4)); // and this boost::shared_ptr<A> p(new A(7)); int j = boost::mem_fn(&A::get)(p); // but how do I do this? // std::vector< WHAT GOES HERE > w; // w.push_back(boost::mem_fn(&A::get)); // int k = w[0](p);
return 0; }
I do not know if mem_fun supports the boost::result_of template, but if it does that would let you get what you need, and if it does not support it then that needs to be fixed.
On Tue, Sep 1, 2009 at 1:57 AM, OvermindDL1 <overminddl1@gmail.com> wrote:
On Mon, Aug 31, 2009 at 9:33 PM, Lowell McLinskey<lmclinskey@gmail.com> wrote:
I am having trouble understanding the return type of mem_fn. Is it possible to create a vector of this type, analogous to how one can create a vector of type mem_fun_t to hold the return values of mem_fun()? Here is an example of what I'd like to do. Thanks in advance. #include <vector> #include <functional> #include "boost/shared_ptr.hpp" #include "boost/mem_fn.hpp" class A { public: A(const int a) : a_(a) {} const int get() const {return a_;} private: int a_; }; int main(int argc, char** argv) { // I can do this std::vector<std::const_mem_fun_t<const int, A> > v; v.push_back(std::mem_fun(&A::get)); int i = v[0](new A(4)); // and this boost::shared_ptr<A> p(new A(7)); int j = boost::mem_fn(&A::get)(p); // but how do I do this? // std::vector< WHAT GOES HERE > w; // w.push_back(boost::mem_fn(&A::get)); // int k = w[0](p);
return 0; }
I do not know if mem_fun supports the boost::result_of template, but if it does that would let you get what you need, and if it does not support it then that needs to be fixed.
It looks like the documentation indicates that boost::result_of is supported: unspecified-N::result_type is defined as the return type of the member function pointer passed as an argument to mem_fn (R in the following): template<class R, class T> unspecified-2 mem_fn(R (T::*pmf) () const); I'm still not sure what the template parameter should be to make the following work: typedef boost::function_types::result_type< What Goes Here > result_type; std::vector<result_type> w; w.push_back(boost::mem_fn(&A::get)); boost::shared_ptr<A> p(new A(7)); int k = w[0](p); // k = 7 I was able to deduce from compiler errors something that does actually work, but it doesn't seem very intuitive: boost::shared_ptr<A> p(new A(7)); std::vector<boost::_mfi::cmf0<const int, A> > u; u.push_back(boost::mem_fn(&A::get)); int n = u[0](p); // n = 7
AMDG Lowell McLinskey wrote:
I am having trouble understanding the return type of mem_fn. Is it possible to create a vector of this type, analogous to how one can create a vector of type mem_fun_t to hold the return values of mem_fun()?
The return type of boost::mem_fn is unspecified. You have to use either boost::function or (on compilers with a native implementation) BOOST_TYPEOF. In Christ, Steven Watanabe
participants (2)
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Lowell McLinskey -
OvermindDL1 -
Steven Watanabe