c++ - Having a single method in a base class able to allocate for child classes -
i'm trying have common base/helper class allocates shared_ptrs calling class, i'm having problems getting work in derived classes.
#include <memory> template<typename t> struct spalloc { virtual ~spalloc() {} template<typename ...args> static std::shared_ptr<t> alloc(args&&... params) { return std::make_shared<t>(std::forward<args>(params)...); } template<class u, typename ...args> static std::shared_ptr<u> alloc(args&&... params) { return std::make_shared<u>(std::forward<args>(params)...); } }; class base : public spalloc<base> { public: virtual ~base() {}; }; class child : public base { public: virtual ~child() {}; }; typedef std::shared_ptr<base> pbase; typedef std::shared_ptr<child> pchild; int main() { pbase base = base::alloc(); pchild child = child::alloc(); } i understand class base : public spalloc<base> means t in template going base, why created second alloc. second alloc needs called child::alloc<child>().
is there way write alloc compiler can deduce class i'm calling alloc with?
short answer: no, there isn't.
long answer: point alloc not aware of child unless explicitly told, information come from? call child::alloc() call base::alloc(), call spalloc<base>::alloc() , there, information child lost.
the easiest solution using free function, function exists , it's called: std::make_shared. maybe consider using directly , safe trouble spalloc altogether.
alternatively, if want overwrite spalloc<t>::alloc() each child, won't need base class spalloc @ all, add method each class, that's easier using base class.
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