std::shared_ptr<T>::operator=

cppreference std::shared_ptr::operator=

NOTE: 原文对于各种assignment operator给出了其对应的**Equivalent** ，可以看到，这些**Equivalent**都用到了swap，显然这是在使用copy and swap idiom

(1)

shared_ptr& operator=( const shared_ptr& r ) noexcept;

template< class Y >
shared_ptr& operator=( const shared_ptr<Y>& r ) noexcept;

Shares ownership of the object managed by r. If r manages no object, *this manages no object too. Equivalent to shared_ptr<T>(r).swap(*this).

NOTE: 此处的share，就是在前章节中提及的acquire；

(2)

shared_ptr& operator=( shared_ptr&& r ) noexcept;

template< class Y >
shared_ptr& operator=( shared_ptr<Y>&& r ) noexcept;

Move-assigns a shared_ptr from r. After the assignment, *this contains a copy of the previous state of r, and r is empty. Equivalent to shared_ptr<T>(std::move(r)).swap(*this).

(4)

template< class Y, class Deleter >
shared_ptr& operator=( std::unique_ptr<Y,Deleter>&& r );                    

Transfers the ownership of the object managed by r to *this. The deleter associated to r is stored for future deletion of the managed object. r manages no object after the call. Equivalent to shared_ptr<T>(std::move(r)).swap(*this).

NOTE: 这就是std::unique_ptr to std::shared_ptr，在下面的章节描述了这个内容:

1、learncpp M.7 — std::shared_ptr