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#include <iostream>
#include <memory>
#include <string>

template <class T>
std::shared_ptr<T> make_instance();

template <class T> requires std::is_default_constructible_v<T>
std::shared_ptr<T> make_instance()
{
    return std::make_shared<T>();
}

template <>
std::shared_ptr<int> make_instance()
{
    return std::make_shared<int>(25);
}

template <>
std::shared_ptr<std::string> make_instance()
{
    return std::make_shared<std::string>("abc");
}

struct A { std::string val; };

int main()
{
    std::shared_ptr<int> p_int = make_instance<int>();

    std::shared_ptr<std::string> p_string = make_instance<std::string>();

    std::shared_ptr<A> p_a = make_instance<A>();

    std::cout << *p_int << ", " << *p_string << std::endl;
}