deduction guides for std::shared_ptr

From cppreference.com
< cpp‎ | memory‎ | shared ptr
Memory management library
(exposition only*)
Uninitialized memory algorithms
(C++17)
(C++17)
(C++17)
(C++20)
Constrained uninitialized
memory algorithms
(C++20)
C Library

Allocators
(C++11)
(C++11)
Memory resources
Garbage collection support
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
Uninitialized storage
(until C++20*)
(until C++20*)
(until C++20*)
Explicit lifetime management
Defined in header <memory>
template < class T >
shared_ptr( std::weak_ptr <T> ) - > shared_ptr<T> ;
(1) (since C++17)
template < class T, class D >
shared_ptr( std::unique_ptr <T, D> ) - > shared_ptr<T> ;
(2) (since C++17)

These deduction guides are provided for std::shared_ptr

Note that there is no class template argument deduction from pointer types because it is impossible to distinguish pointers obtained from array and non-array forms of new

Example

#include <memory>
 
int main()
{
    auto p = std::make_shared<int>(42);
    std::weak_ptr w{p};    // explicit deduction guide is used in this case
    std::shared_ptr p2{w}; // explicit deduction guide is used in this case
}