P22: Member Templates

A template inside a template, usually used in constructors,

• Use grass carp and sparrow to initialise the fish class and the bird class (passed in to the constructor)
• T1 first works here because first is a grass carp, which inherits from the fish class; this is also called an up-cast

// for smart pointer
template<class _Tp>
class shared_pte:public _shared_ptr<_Tp>{

    ...
    template<class _Tp1>
    explicit shared_ptr(const _Tp1* _p):_shared_ptr<_Tp>(_p){}
}
shared_ptr<Base1>sptr(new Derived1);

• To make constructors more flexible