c++11 - How do I implement polymorphism with std::shared_ptr? -

i have seen of other questions on topic, have still not found answer - guess i'm missing something:

i defined 2 simple test classes:

class testbase {    public:      testbase ( ) { };     ~ testbase ( ) { };    protected:      inline virtual int getint ( )     {         return 0;     }  };  class testderived : public testbase {    protected:      inline int getint ( ) override     {         return 1;     }  }; 

i declared typedefs simplify usage std::shared_ptr:

typedef std::shared_ptr<testbase> spbase; typedef std::shared_ptr<testderived> spderived; 

problem: cannot compile code use these shared_ptr declarations polymorphically, though base in these cases instance of spderived:

spbase base; spderived derived = static_cast < spderived > ( base ); 

error: no matching function call ‘std::shared_ptr::shared_ptr(spbase&)

spderived derived = dynamic_cast < spderived > ( base ); 

error: cannot dynamic_cast ‘base’ (of type ‘spbase {aka class std::shared_ptr}’) type ‘spderived {aka class std::shared_ptr}’ (target not pointer or reference)

spderived derived = static_pointer_cast < spderived > ( base ); 

error: conversion ‘std::shared_ptr >’ non-scalar type ‘spderived {aka std::shared_ptr}’ requested

spderived derived = dynamic_pointer_cast < spderived > ( base ); 

error: conversion ‘std::shared_ptr >’ non-scalar type ‘spderived {aka std::shared_ptr}’ requested

i'm using c++11 on ubuntu 14.04 box default gcc tool chain. compiler gcc-4.9. doing wrong? can't shared_pointer used polymorphically?

a type passed in std::static_pointer_cast , std::dynamic_pointer_cast first type template argument type of converted pointer's type itself, not of smart pointer type:

static_pointer_cast<t>(arg);                 .~~~^                   v  template <class t, class u>             .~~~~^              v  shared_ptr<t> static_pointer_cast(const shared_ptr<u>& r);   dynamic_pointer_cast<t>(arg);                 .~~~~^                   v  template <class t, class u>             .~~~~^              v  shared_ptr<t> dynamic_pointer_cast(const shared_ptr<u>& r); 

with said, call below:

spbase base = std::make_shared<testderived>(); spderived derived = std::dynamic_pointer_cast<spderived::element_type>(base); // or: spderived derived2 = std::dynamic_pointer_cast<testderived>(base);