The task is to write one_edit_apart function that determines is it possible to make two given strings equal by replacing, adding or removing one symbol. The equal strings are considered to be equal, for example:

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

The task is trivial, but Yandex interviewers require all the calculation to be done exactly in their inline editor without debugging and compiling and they do not accept the solution until it works for all possible input. The obvious solution is to truncate equal heads and equal tails and check if the lengths of remaining strings are not greater than 1, but if you forgot to handle the case when heads and tails intersect (with “a” and “aa”, for example) they will say “ooops…., you did a newbie mistake that 1-st year students usually do” and if this all takes more than 40 minutes you fail to pass the test. Below I provided the source code they are most likely to accept:

The compiler deduces U as std::string& or as std::string depending on value category of the argument:

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;
}

At least this compiles and works:

#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>();
}

There is no difference between lines 82 and 92 in the code below with both MSVC2022 and GCC11:

#include <utility>
#include <stdexcept>
#include <iostream>

struct Object
{
    virtual const char* name() = 0;

    virtual ~Object() = default;
};

struct A : public Object
{
    const char* name() override
    {
        return "A";
    }
};

It converts only from non-virtual base class subobject:

struct B
{
    virtual ~B() {};
};

struct D : public virtual B { };

int main()
{
    D d;
    B& br1 = d;

    // cannot convert a 'B*' to a 'D*'; conversion from a virtual base class is implied
    // static_cast<D&>(br1); 

    dynamic_cast<D&>(br1);

    return 0;
}

In the vernacular they say stack and heap, but the standard call this automatic and dynamic: