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deduction guides for std::weak_ptr - cppreference.com

From cppreference.com

template< class T > weak_ptr( std::shared_ptr<T> ) -> weak_ptr<T>;

 (since C++17)

One deduction guide is provided for std::weak_ptr to account for the edge case missed by the implicit deduction guides.

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
}