#include <iostream>

int main()
{
    auto a = "str";
    const auto& ar = "str";
    const char* b = "str";
    auto const &c = a;
    auto* d = &a;
    const auto e = 2;

    static_assert(std::is_same_v<const char(&)[4], decltype("str")>);
    static_assert(std::is_same_v<const char*, decltype(a)>);
    static_assert(std::is_same_v<const char(&)[4], decltype(ar)>);
    static_assert(std::is_same_v<const char* const&, decltype(c)>);
    static_assert(std::is_same_v<const char**, decltype(d)>);
    static_assert(std::is_same_v<const int, decltype(e)>);

    std::cout << "a: " << typeid(a).name() << std::endl;
    std::cout << "ar: " << typeid(ar).name() << std::endl;
    std::cout << "b: " << typeid(b).name() << std::endl;
    
    return 0;
}

#include <iostream>
#include <sstream>

template <class C>
class basic_format
{
public:
    
    template <typename T>
    basic_format & operator << (const T & val)
    {
        out << val;
        return *this;
    }

    std::basic_string<C> str() const { return out.str(); }

    operator std::basic_string<C>() const { return str(); }

private:
    
    std::basic_ostringstream<C> out;
};

one_edit_apart("cat", "at") == true
one_edit_apart("cat", "cats") == true
one_edit_apart("cat", "cast") == true
one_edit_apart("cast", "cats") == false
one_edit_apart("cat", "cut") == true
one_edit_apart("cat", "dog") == false

template <class U>
void f(U&& s)
{
    static_assert(std::is_same_v<U, const std::string&>);

    std::cout << std::forward<U>(s) << std::endl;
}

int main()
{
    const std::string& s = "abc";

    f(s);

    return 0;
}

#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>();
}