c++ - typedef with CRTP doesn't work when inheritance is used -

c++ - typedef with CRTP doesn't work when inheritance is used -

is there ways define type same name classes in inheritance relationship using ctrp? tried next code got error: fellow member 'ptr_t' found in multiple base of operations classes of different types clang++.

#include <iostream> #include <tr1/memory> template <typename t> class pointable { public: // define type `ptr_t` in class `t` publicly typedef std::tr1::shared_ptr<t> ptr_t; }; class parent : public pointable<parent> { public: parent() { std::cout << "parent created" << std::endl; } ~parent() { std::cout << "parent deleted" << std::endl; } }; class kid : public parent, public pointable<child> { public: child() { std::cout << "child created" << std::endl; } ~child() { std::cout << "child deleted" << std::endl; } }; int main(int argc, char** argv) { child::ptr_t child_ptr(new child()); parent::ptr_t parent_ptr(new parent()); homecoming 0; }

of course, next 1 ok (but it's redundant , go against dry principle).

class parent { public: typedef std::tr1::shared_ptr<parent> ptr_t; parent() { std::cout << "parent created" << std::endl; } ~parent() { std::cout << "parent deleted" << std::endl; } }; class kid : public parent { public: typedef std::tr1::shared_ptr<child> ptr_t; child() { std::cout << "child created" << std::endl; } ~child() { std::cout << "child deleted" << std::endl; } };

if there no ways accomplish behavior using crtp, why prohibited?

your problem has nil crtp, multiple inheritance. child inherits ptr_t both base of operations classes, , both types different: shared_ptr<parent> vs. shared_ptr<child>. therefore, compiler cannot figure out type mean child::ptr_t in main.

as pointed out, have prepare manually using typedef in child (making pointable base of operations class useless, though).

class kid : public parent, public pointable<child> { public: typedef pointable<child>::ptr_t ptr_t;

c++ inheritance crtp