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deduction guides for std::shared_ptr

From cppreference.com
< cpp‎ | memory‎ | shared ptr
 
 
Memory management library
(exposition only*)
Uninitialized storage (until C++20)
(until C++20*)
(until C++20*)

(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)
 
std::shared_ptr
Member functions
Modifiers
Observers
(until C++20*)
Non-member functions
(until C++20)(until C++20)(until C++20)(until C++20)(until C++20)(C++20)
functions (until C++26*)
Helper classes
Deduction guides(C++17)
 
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 to account for the edge cases missed by the implicit deduction guides.

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.

[edit] Example

Run this code
#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
}
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