When creating a std::unique_ptr in C++, one usually passes the extra delete functor as the template parameter.
But std::shared_ptr needs it as the constructor parameter.
The answer1 explains that std::unique_ptr binds the deleter to its type to avoid the runtime overhead of an indirect call for the deleter.
std::shared_ptr binds it at runtime to make it easier for users to override the deleter2.
template< class Y, class Deleter >
shared_ptr( Y* ptr, Deleter d );Note by default, the default deleter is std::default_deleter<T>3 :
template<
class T,
class Deleter = std::default_delete<T>
> class unique_ptr;