Why is std::make_shared<T> not a static function of std::shared_ptr<T>, i.e. std::shared_ptr<T>::make?

Question

This is a question about understanding a design decision, not a complaint about bugs or flaws.

In the C++ standard library, the function to create a shared pointer and its object is a straight function,

template< class T, class... Args> std::shared_ptr<T> make_shared( Args&&... args );

Why is this function not a static function of shared_ptr<T>, like this:

template <class... Args> std::shared_ptr<T>::make(Args&&... args);

This would keep the std:: namespace a little tidier, and would also allow for something like this:

using shared_vector = std::shared_ptr<std::vector<int>>;

shared_vector a = shared_vector::make(7);

Answer 1

The only rationale given in the proposal for std::make_shared, document N2351, is that it makes it possible to add the functionality non-intrusively to any already existing implementation of shared_ptr.

std::make_shared was added to the standard draft after std::shared_ptr itself and there had been prior shared_ptr implementations, e.g. in boost.